Losing the EA game franchises from their console platforms would be very damaging to Microsoft or Sony as it would result in a loss of console sales, especially with the Madden (and other sports games) and The Sims. If EA dropped the Xbox, Sony would fall over themselves to keep them onside.
It would be so damaging that if Microsoft got wind of Apple going for a major games publisher I'd be very surprised if they didn't get involved in a bidding war. Unless they got their fingers burned too badly with previous purchases - they must of gone done for a small fortune with Rare.
Other than to declare war on Microsoft, I'm not sure there is many other benefits. There are far better ways to get more games on Apple platforms, better platforms, better selling platforms, better development kits and so on. If they get all of that right the developers will come to them.