verification of one account only?

Not entirely true either. I have one avatar. She goes everywhere, does everything. No alt required.

I think it is more accurate to say that if you can't seperate RL from SL, or if you see your avatar as an extension of your RL self, then it is unlikely that you would see any need for more than one account.

Others may only have a need for one acount, for what they do in SL. That's fine, for them.

But roleplayers and people in businesses may have many reasons to have multiple accounts. As a content creator and builder, my alts are invaluable for testing permissions on my creations and on the builds I set up. As a roleplayer, many of my alts are the characters in the interactive storytelling that I percieve roleplay as. And as a heavy user of SL, some of my alts are the only way I can retain membership in all the groups I need/want to keep track of. For example, my main avatar is required to be in a lot of land groups, for my work as a sim designer. I don't have room for groups for my favorite fashion designers, content creators, or product support/update groups. I have to assign those to some of my alts.