Could be tough, but not impossible for GT5

So it will be close... I can't predict who will win.

Well not sales wise but quality wise. Granted many issues were fixed in the XL version. It's kind of like FF13. That game turned out to be pretty mediocre in the eyes of many yet it is still one of the highest selling Final Fantasy games. So much so that Sqaure thinks that we actually wanted there to be 3 games in the universe. 

I think it's actually amazing how popular FPS games have become this gen. Halo has seen massive growth due to not only the increase in the installbase for the 360 but also a rise in interest in the FPS genre as a whole.

If you take a look at the software sales per genre :

PS3: 138 million shooters

PS3: 56 million racing games. 

360: 221 million shooters

360: 54 million racing games.

So 359 million shooters sold this gen so far on the HD twins, 110 million racing games. It's simply a much, much bigger genre. (Even if you add the Wii, DS and PSP racing games to the tally, it's not even comparable.)

There is way way way more FPS than racing games... especially simulators.

Well it took them 5 years to develop and finally ship the game. Taking advantage of the fact it sold well and they could use the available assets to push out a few sequels on a faster schedule is a strong business decision, which unfortunetly will always weigh more importantly than the creative direction of a franchise.

The ones who prefer sony over MSFT.  

And yes it is better to have a game front lopaded because that means more profits.

Well the point I was trying to illustrate is that there is a much bigger market for shooters. A larger portion of gamers want them over the likes of racing games and while there are a few exceptions of high selling racing games (GT and MK for example) this gen has predominatly been dominated by shooters. If the increase of this trend were to continue next generation, it should be of no surprise that more and more FPS games will outsell the few high profile racing games.

I'd imagine a combination of the two is probably the best for most titles. Simply having the game sell 90% of it's total in one week puts money in the bank, but leaves little sustained income. If the game is big enough though, as is the case here with both titles, that of course doesn't matter really as the inital return will cover everything.

Disregarding profits and business etc. It's far more fun watching games with great legs leg it over milestones.

Still don't see where people are getting that Halo doesn't have legs but the reason for front loaded preferred games for companies is because the majority of the sells money is coming from full retail price instead of bargain bin price.