The market buying 7+ year old consoles at ~$200 is not the same as those buying them at launch for $4-500. Microsoft and Sony will be going after consumers who have owned a 360 or PS3 for years. As for GTAV, as popular as it will be, it will likely sell to less than 20% of the 360/PS3 userbase. Plus it is out around two months before the new consoles.
That isn't to say the new consoles have will have guaranteed success, but I don't think these would be the reasons. A bigger factor would probably be that nearly all the third party games will be coming out on the 360/PS3 as well this holiday.







