Actually, PayPal does this with its merchants systematically.

The frozen funds all get pooled, and PayPal earns interest off the cash while the funds remain frozen.  So they have a certain motivation to freeze accounts, then require their users to justify their existence with all sorts of paperwork they never mentioned upon sign-up.  For instance, a utility bill that must be in your name.  Not all of us have that.

In short, they're not happy until you're not happy.

The primary reason people use them as the standard is because they heard about PayPal through the mainstream media outlets.  Those media outlets are essentially owned by the same few megacorporations, so what they hype vias the media determines what the majority of people use - until people can discover a better alternative.  Thus sites like Facebook and Google, both the bastard offspring of C.I.A.-based investment firm In-Q-Tel, have become what the mainstream use.  Never mind that they work closely with the Information Awareness Office, which actively compiles data on users and tries to keep it all cross-referenced in its own databases for easy domestic snooping of citizens.  It's the federal government's approach to using commercial entities to get around the Fourth Amendment safeguard against unreasonable search and seizure, with a fair amount of tycooning and market manipulation thrown in for good measure.

Well, I say "good" measure...