It seems everything is in Beta these days and it seems to stay there, and as dead2.0 points out Google has been a key culprit in making the term meaningless. Read the post for a good breakdown of what beta should and used to mean (and the comments for a little more colour on who first started to abuse it).
My point here is that it has become meaningless. If everything is in beta the term is redundant.
I think people persist with it for marketing purposes. In the early days of Gmail and ICQ the notion of beta was used to imply some kind of exclusivity and spread the services virally. And very successfully too.
But isn’t it time for something new now?
These things stop working when people see them for what they are. When you can read about them in books like The Naked Conversation then surely it is time to move on.
I have just found this Museum of Modern Betas which seems to confirm that the term is over-used.