I'm one who signed up for PS3 beta, but I will also buy the PC version to play first release. Here's my thought:
Why not have the PS3 Beta on live servers? What I picture is that those who, like me, will be playing the PC version of the game while waiting for the PS3 release, have the opportunity to test the PS3 client as well.
My assumption (and it may be assinine, as I have no knowledge whatever of programming) is that if the beta client for the PS3 is jacked up, it just means that your client crashes, not the server. In that sense, the only immediate harm to performing like this is to the player "testing" on the PS3 and any groupmates. For someone like me who will play the PC version out of raw desire to play earlier but who still truthfully wants to play on the PS3, this seems like the most apt way to test this. If I get into the PS3 beta while I'm already playing the PC release version, what incentive do I have to give up "real" play time in order to test the PS3 client when I could be playing my permanent character(s)?
It seems to me that the most prudent way to get legitimate PS3 beta testing would be to allow me to play my live character on a live world.