I think this trend is disturbing. I've seen a few "revenge revisions" here over the past few days, and though I understand the frustration of not getting paid (I've been freelancing for 8+ years), this is not the way to deal with the problem.

I'm a big fan of using a staging server that I'm in control of for changes to sites. We'll agree on a scope for an individual project or revisions, then I'll make the changes on my server and send you a link. If the changes are to your liking and the scope has been met, I'll bill you. Upon receipt of payment, I'll upload the changes to your live site, and we'll start again ad infinitum.