The Ultras replaced the non-Ultras.
As far as I know, the only changes were:
-- higher quality amplifier (previous ones gave out alot)
-- drivers painted white instead of black
-- new horizontal volume control box instead of vertical
Some other changes may have been made, but I am unaware of them.
The Ultra or non-Ultras are great values though, both as stand alone sets and for upgrades. The subwoofer apparently is comparable to the RW-8 (although with slightly less bracing), which alone is a $250 product. In addition to a great sub you get a powerful satellite amplifier built into the subwoofer (not available in most stand alone subs), and a few decent sateliites. The only downfall is that the sub itself has no variable low-pass filter or phase control.