That's because the demos at E3 were pre-rendered, not rendered in real-time like the Xbox 360.
Reports say that when both consoles were running with their Alpha Development Kits, the 360 was pushing out about 20-30% of it's effort, while the PS3 was pushing out about 60-70%. While these aren't confirmed, it just gives you a heads up about the 360's power and potential in the next-gen market. Microsoft has made it a proven competitor against Sony and their Playstation, although Ken Kutaragi a.k.a the Pompous Ass, attacks it with cheap remarks, while Microsoft attacks the PS3 with true honest to god hardware comparisons, not jibber jabber
About Nintendo, no one knows about Nintendo! They're the underdog, and I frankly could careless if they went bankrupt. Them and their fanatical ideas are going to make the Revolution gain just as much popularity as the Gamecube (which isn't that much). Although I would give kudos to the Revolution's size.