History of this gen certainly supports your case ioi. I think you've made the most logical conclusion based on data but I'd argue that PS3 has had weak holiday seasons because it was an overpriced console lacking huge games. Now that has changed and I believe we're going to see a different PS3 sales wise. I don't think it would drop as fast as you do if there were no new releases. You're treating PS3 like it was the same console it was a year ago that just had a temporary boost and I'm treating it as a re-branded console that's going to have a different set of legs in the sales market. I could be way off but that's my best prediction as of now.
I agree that Wii has the stronger lineup but I don't know if that is going to equal higher software sales. Wii Sports and Wii Fit will sell like crazy but are they going to bring in people that didn't play the original games in the series? It comes down to Mario vs Final Fantasy and I think the power of Final Fantasy is seriously being underestimated here. Now I'm gonna go look at some old data to get a better feel for this, I admit I made my prediction based on memory and didn't bother to look stuff up.