The difference is that they own the Frame Relay network and can control
provisioning etc. Your experience with Frame Relay has been colored by
the fact that your Telco is in control of the Frame Relay "Cloud".
As several others have stated in the list here UUNET is using it to
aggregate users into POP routers and to switch packets across the
backbone as much as possible and route only when necessary. The
problems they seem to be having now are due (possibly) to some problems
with the software in the BSTDX switches and probably their own success.
It is pretty tough to grow a network like theirs quickly enough to keep
up with the overall growth of the Internet without some problems.
That said I hope they get it fixed soon. They were, at one time, our
best provider and they have slipped to our worst.