It would help Microsoft, yes. But if Microsft bought Sega and put all their old games on Xbox live arcade, I'd be really pissed, since i JUST bought a Sega Saturn :(
On the whole I think Sega was sorta the violent rebel company, with rebelious Sonic to appeal to kids. I think it would be better if Nintendo somehow bought the Sonic franchise and Sonic team and Microsoft got the rest. But I don't see how that would ever happen.
Buying Sega would really beef up Micrsoft's 1st party. I think that if they bought SE as well, they would be able to come in a strong 2nd in the console war. They could cancel Dragon Quest 9 for DS and put it on the 360 lol







