Starcraft, there are a few too many assumptions in your original post for me to hop on board with your thesis. To begin with, I think there's a less-than-even chance that we'll be seeing a 360 price drop this summer. Microsoft Corporation needs money (there's a sentence you never thought you'd hear!), and Microsoft's gaming division needs to start proving its worth very soon for the impatient investors, many of whom were skeptical about the X-Box line from the get-go and who have begun to demand that it shut down. Microsoft is wisely aiming for profitability right now, and a price drop won't really help too much in that regard. And yes, there are rumors about a price drop going around, but that just makes it another week on the internet, doesn't it?
As you yourself have said, Gears 2 is not going to move many consoles, as the system already has the original game. I'm highly skeptical about the value of Too Human, which doesn't look too hot gameplay-wise and which is virtually unknown outside of the most devoted of internet forums. Left 4 Dead has some potential, but I think most people who are really interested in Valve's works still see them as a PC company, and will buy the product there: sales of the Orange Box on the 360 are healthy, but they're almost certainly dwarfed by those on the PC.
That leaves two games. The original Fable sold on a mountain of hype as being the greatest RPG ever: when people actually played it, many were underwhelmed. While the sequel may be better, it'll take time for word of mouth to spread the news, so if it has an effect on console sales, it'll be a minor bump spread out over several months. I'd also like to point out that I haven't heard too much excitement about this game outside of X-Box fans. Banjo might maybe have some effect, but it'll be at launch rather than before, since of the two types of people it might attract X-Box fanatics already own a 360, and "casual" fans rarely buy a console before a game releases. The fact that this title again is unknown outside the internet does not help you case.