I'm pretty sure it's not going to happen this time.
You also have to remember that vista was a huge marketing flop, so they really did kind of sweep it under the table the second 7 was on the market.
With 7 to 8 though, 7 has been very popular a lot of people like it, and just about everything supports it at this point. I don't see it sliding off as fast as vista did.
I'm sure someone here will probably give you a nice graphic or something to go on.