As seen in the video at the conference, I'd say there might be a hole new thing to it;
You can connect an account to your 'personal' profile (like a facebook profile), and then those 2 accounts are linked.
Sony wants to make PS4 more social, so yeah, but thats just my thought on it.
In the video, wich I watched at 2/3 AM in the night so I'm sorry if I'm wrong, I did see PSN names linked to such a 'personal' account, and I think I also saw they had the same standard avatars on the PSN's as we do now. This leads me to the conclusion that we will have the same PSN accounts. But once again, it was late
.
Sorry if I don't make any sense, I'm not English.