Robert - really? This is a surprise.
Jokes aside, I don't see a problem with that move. We aren't a press gang forcing people into joining or staying.
It does call into question the purpose of OASIS. Some of us say we want contributors or get out. Others say it's ok to be a lurker.
I would imagine if someone is dropping down from 90 Minds to OASIS, it's either a realization of lower participation or they don't see the value for the $$$. I have a hard time believing the latter though.