let me explain this to you in a way which is easier for us car guys to understand.
Lets say the PS3 is the Mark VIII and Xbox 360 is the Eldorado. We all know they are both great cars that are equally fast but the Elorado(xbox) requires much more attention then the Mark VIII(PS3). Most Eldorado(xbox) have an issuse with overheating as is the case with the Xbox. When you have an Eldorado, the question isn't "Will my northstar engine need an Head Gasket job?" But "When will it blow its Head Gasket?" So what I am trying to say is, Xbox is gonna get the red ring of death sometime.
Now to Online
So now that you got your Mark VIII(PS3) or Eldorado(Xbox) you know you are gonna drive it even if you say it is going to be your weekend toy. Well every month or so you are going to go to walmart and buy a $5 Quart of oil for your Eldorado just like you would have to pay for online for the Xbox. I now you wouldn't like to pay $5 just to enjoy your full capability of your car. That is where the Mark VIII (PS3)shines, you don't need to put more money into it like the Eldorado(xbox) because the online is FREE. I can guarantee you will be online most of the time.
Now the Features
Mark VIII (PS3) hands down beats the Eldorado (Xbox) on features like the power telescoping steering wheel, Xenon lights....etc. Just like the PS3 has Blu ray, WiFi, Bluetooth....etc.
Now mods are like games for these gaming consoles. So the Eldorado, you will only be able to do stuff like Exhaust, CAI, and maybe little things here and there. just like for the XBox you have Halo, Gears of war and the some old stuff. Now the Mark VIII(PS3), you can mod it with many different things like Gears, Supercharger and much more just like the variety PS3 offers Resistance 2, Killzone 2, MAG, Little big planet, infamous and much more.
Oh and the PS3 can also have netflix BTW
Hope you can decide which you want but I am sure your will make the right choice as I see you have a Mark VIII.