So if it's not as easy for you to buy a brand new console why do you assume it's easy for others to buy it? They cost money, money that quite frankly could be put to better use than buying a new console. If a 360 owner really wanted a PS3 they would have bought one already. To me buying a new console is like an investment. I want to make sure I'm gonna be getting my money's worth. If there's nothing I'm interested in, I won't buy it. Not out of brand loyalty (which in my eyes is a stupid reason for not buying a console) but because I would like my money to be well spent. That is the reason why we won't go out and buy a brand new console for one game. And for the record I'm actually a 360 owne which I've already said.
To answer your question: no, simply because exclusive content is not enough to make me fork out £200 on a new console. I wouldn't be that bothered about it. Sure I'd be disappointed but I wouldn't demand Ubisoft give it to the other console. Clearly this has bothered you. The best thing to do would be to create a petition on the AC3 boards to get it's exclusive content released on the 360 (which it no doubt will do after a month or so anyway). Getting all up in arms about something that will come to you sooner or later is just baffling. There's no point.
I haven't bought a PS3 yet simply because the games that I'm interested in playing, aren't enough to make me spend my hard earned money on one. The Last of Us has changed all that. That is a game that I have to play. So I will buy a PS3 for that game but it won't be the only game that I'll play. Same goes for the 360. If Watch Dogs was exclusive to the 360 and I had a PS3, I would buy a 360 in a heartbeat in order to play that game but first I'd make sure there was other games I'm interested in.