Prior to the launch of Rockstar's Grand Theft Auto IV this year, some analysts thought that the game could become the best selling game of 2008. Hudson Square Research's Daniel Ernst forecast total sales of 13 million copies, edging out Nintendo's Wii Fit with a forecast of 10 million units sold.

Now, however, it looks like GTA IV may not have the momentum to cross the finish line; Wii Fit (like the Wii itself) on the other hand remains very much in demand. While GTA IV made a huge splash at launch, selling around six million units in the first week and grossing $500 million worldwide, sales of the latest GTA slowed considerably in the months following.

As of late August, according to a joint report from The NPD Group, GfK Chart-Track Limited in London and Enterbrain in Japan, GTA IV had sold around 6.3 million units compared to Wii Fit at 3.6 million. In the U.S., NPD charts show that Wii Fit continues to make the top 10 selling titles, while GTA IV is nowhere to be seen in the top 20. Wii Fit was number four in August and number two in September. Looking at the U.S. only, NPD told us that life-to-date GTA IV has sold 4.86 million units (all versions including LE), while Wii Fit sold 2.34 million units.

"Wii Fit is attaching at around a 30 percent rate, so I suppose if that continues, it will outsell GTA," Wedbush Morgan's Michael Pachter told GigaOM. While GTA IV appeals to the traditional video game audience, Wii Fit is targeting a broader demographic, and it's one of those titles, like Wii Play, that is essentially evergreen. With the Wii being in high demand, anytime a consumer picks up a new Wii, he/she is likely to purchase one or both of these games.

Pachter noted that Wii Fit outselling GTA IV is "less of a comment on GTA than a comment on the potential for other games to thrive." In particular, Pachter is optimistic for the potential of the Balance Board peripheral: "I consider Wii Fit more of a platform than a game, as I think the compelling feature is the potential for other games like Shaun White, Rayman, or even a new Tony Hawk game. And don't forget Jillian Michaels Fitness."

Wii Fit Screens

Screens from Nintendo's Wii Fit

Shigeru Miyamoto - Photo Gallery

    A famous video game creator for Japanese video game giant Nintendo, Shigeru Miyamoto, demonstrates how to use the new fitness video game on the new balancing board controller for the company's video game console Wii in Chiba, suburban Tokyo, 10 October 2007. Nintendo will launch the new fitness video game softwarer WiiFit including the balancing board controller on 01 December.

    YOSHIKAZU TSUNO/AFP/Getty Images

    A famous video game creator for Japanese video game giant Nintendo, Shigeru Miyamoto, demonstrates how to use the new fitness video game on the new balancing board controller for the company's video game console Wii in Chiba, suburban Tokyo, 10 October 2007. Nintendo will launch the new fitness video game softwarer WiiFit including the balancing board controller on 01 December.

    YOSHIKAZU TSUNO/AFP/Getty Images

    The famous video game creator for Japanese video game giant Nintendo, Shigeru Miyamoto, displays the new balancing board controller for the company's video game console Wii in Chiba, suburban Tokyo, 10 October 2007. Nintendo will launch a new fitness video game software WiiFit, including the balancing board controller on 01 December.

    YOSHIKAZU TSUNO/AFP/Getty Images

    The famous video game creator for Japanese video game giant Nintendo, Shigeru Miyamoto, displays the new balancing board controller for the company's video game console Wii in Chiba, suburban Tokyo, 10 October 2007. Nintendo will launch a new fitness video game software WiiFit, including the balancing board controller on 01 December.

    YOSHIKAZU TSUNO/AFP/Getty Images

    Tokyo, JAPAN: Nintendo's Shigeru Miyamoto displays the remote control of the new video game console 'Wii' at a press preview in Tokyo. Nintendo recalled 3.2 million wrist straps for its new Wii console ,15 December 2006, after reports of enthusiastic users inadvertently sending the motion-sensing controller crashing into their TV screens.

    YOSHIKAZU TSUNO/AFP/Getty Images

    Tokyo, JAPAN: Japan's video game giant Nintendo game creator Shigeru Miyamoto (L), known as the father of Super Mario, and President Satoru Iwata playing a tennis game during a demonstration at a press conference in Tokyo. The Japanese electronic game maker Nintendo said Friday 15 December 2006 it was not recalling motion-sensing controllers for its new Wii model but would exchange wrist straps that have broken inadvertently. 'Nintendo is not recalling wrist straps furnished with the motion-sensing remote control unit for its new computer game Wii,' the company said in a French-language statement received in Paris.

    YOSHIKAZU TSUNO/AFP/Getty Images

    Nintendo's Wii Games Console To Go On Sale In Europe
    TOKYO - DECEMBER 7: Nintendo president Satoru Iwata (R) and software creator Shigeru Miyamoto (L) demonstrate game Wii during a press conference on December 7, 2006 in Tokyo, Japan. Wii will go on sale on December 8 in Europe.

    Junko Kimura/Getty Images

    Nintendo's Wii Games Console To Go On Sale In Europe
    TOKYO - DECEMBER 7: Nintendo president Satoru Iwata (L) and software creator Shigeru Miyamoto (R) present the Wii game console during a press conference on December 7, 2006 in Tokyo, Japan. Wii will go on sale on December 8 in Europe.

    Junko Kimura/Getty Images

    Nintendo's Wii Games Console To Go On Sale In Europe
    TOKYO - DECEMBER 7: Nintendo president Satoru Iwata (L) and software creator Shigeru Miyamoto (R) present the company's new remote games console, Wii, during a press conference on December 7, 2006 in Tokyo, Japan. Wii will go on sale on December 8 in Europe.

    Junko Kimura/Getty Images

    Tokyo, JAPAN: Japan's video game giant Nintendo President Satoru Iwata (L) and the company's game creator Shigeru Miyamoto, known as father of Super Mario, shows a controler from Nintendo's new video game console 'Wii' at a press conference in Tokyo 07 December 2006. Nintendo said 15 December 2006 that it will recall 3.2 million hand straps for its new Wii games console after reports of users inadvertently throwing the motion-sensing controller into their TV screens.

    YOSHIKAZU TSUNO/AFP/Getty Images