Last time I checked (I don't know if they fixed this, mine has RRoD and I'm waiting for Microsoft to give me a new one), Xbox can only go on Facebook and Twitter. You can go on both sites AND all the others on the PS3. It has its own web browser. The Xbox doesn't. But before the shitstorm comes back, let me say, all three are great, but the Wii isn't getting enough rep, as it can do one thing the PS3 or 360 can't do; play browser based games without getting all screwy. But what you said makes no sense since the PS3 has better internet capabilities. If the PS3 had the same capabilities as the 360, it would be worse.
Yes. The Wii is better than what some people give it credit for. That little machine can play games from a HDD, use emulators with a simple install, but I do agree it's a bitch to mod if it's your first time doing it.
I tried that when my computer was break and I gave up, the navigator was completely shit. Otherwise the best system to me is currently the WII because there are pretty decent jrpg available in Europe ( Fire Emblem Radiant Dawn and Muramasa the Demon Blade are both great ) and when I want to play a game that isn't a jrpg there a plenty of choice of game accessible to me, to be honest if I wasn't a Tales fan and a Gust's games fan HD systems would be unnecessary to me.
The PS3 browser isn't that bad in my opinion. But if I had to pick between the Wii one, and the PS3 one, I'd go with the Wii one.