The interesting thing about those figures is ODST is not even a year old (only been out since end of september) and it is already over 5m. Which is actually more then any of the PS3 exclusive games.
Personally as i have said before. Things have changed, this gen is not like the last gen. Games that we expected to do well have not done as well this gen. GTA:SA sold nearly 19m units making it one of the most sold games of all time. GTA4 has sold nearly 14m combined on all the formats. MGS1 2 both sold more then MGS4. Final Fantasy 13 sold 5m combined. 12 sold nearly 6m, and 10 sold nearly 8m, all on one console. etc etc
Point is it is hard to predict sales this gen. Games that came out around the peak of PS2 obviously sold a lot, we are yet to see an exclusive PS3 game break the 5m barrier. But what we know for sure is that Halo sells loads. We have to assume Reach will sell more then ODST and be on par at least with Halo 3's sales if not very close.
For GT5 to beat Reach it will need to break game records for this gen. I just can't see that happening.
However i think eventually they will do what they did with Pro Logue and include it with most PS3's for awhile.
To put a bit of context into it even if you add sales of the top 2 PS3 exclusives they are still nearly 3m behind Halo 3 sales.
GT is huge, Halo is gigantic