I really doubt that a lot of the people complaining will even buy a Vita. I doubt even more that if they did, they would need to access multiple PSN accounts on it.
I just don't see the issue. I've always been about personal ownership of my electronics. My brother had an Xbox for years and I just bought my own. We both had our own Gameboy Colors and GBAs as well. Only things we actually shared were a PSX and a Gamecube. I bought my own Wii (well, got it as a birthday gift), PS2, Xbox 360, PSP, and DS. Last thing I want is my precious electronic children to be at the mercy of someone else's care.