The 360 app is terrible. No search function, no chapter breaks, too long loading times between screens and, as you've noticed, no WCW or ECW ppvs. And not even all WWE ppvs (no Wrestlemanias or Royal Rumbles other than the most recent shows). Also, you can't scroll the ppvs by year, only by name. So if I know that Cena had a good match against Umaga in 2007, I have to guess the name of the ppv it was on (out of 40+ generic wrestling event names), rather than jumping to 2007.
I haven't used the 360 as a gaming device in a long time, so when the Roku stick comes out next month, I think I'll finally put my former best friend away in a box (and get this giant white monstrosity out of our living room, to my wife's pleasure).
I have a roku on a much smaller tv in the bedroom, so I've watched what I can in there. Somehow got through three hours of Wrestlemania 20 this afternoon. For all the talk of events 'not feeling like Wrestlemania' that I recall from a decade ago, through the sands of time and lowered expectations (and skipping ladies' events), it's been a relatively entertaining and breezy card. Adhering to the Raw/Smackdown brand split sticks out. No one cared then (besides Smackdown occasionally being left to its own devices and featuring good product, iirc).