Well my favourite is the value of online. PS3's is free and 360's is $60/year.
So if your one of the 200 people that still play only offline games then that doesn't affect you, but if you do then your cheap arcade is now $260, after 2 years its $320 and after 3 years (if you don't get RRoD by then) you've payed $380 for your arcade + online each year.
And if you plan on downloading...well anything you better upgrade your hard drive which is another, what $60? $80? I don't even know. It's something like that. I know the 120gb hard drive is over $100.
So yeah out of the box theres no question - The 360 arcade is half the price. And that's all parents see when picking a console for their kid's birthday/Christmas. But the smart people who look at the value of free online, blu ray, etc then the PS3 is better. I didn't even mention better games.