Maybe look again at the graph. The spike on the Revelator starts at around 14k. The tiny spike on the Illuminator is pretty much insignificant as at that frequency it's pretty much out of the range of audibility, and sound is very directional at those frequency's. So at the listening position, it will be flat with the rest of the response anyways. Either way, the spikes aren't much of a big deal. There's other improvements to the illuminators that anyone who's compared them has heard.
The Illuminator tweeter is simply a better tweeter. They don't come up with a successor to an older design 10 years later, using better technology, just to make a driver that preforms worse than the predecessor. They are all good tweeters, even the tweeters from their classic line. Some of them have been in production since the 80's. They can charge more, because it costs them more to produce. The only people still using the Revelator, are designers who came up with their designs before the illuminator came out.
Lots of manufacturers still use the revelator midwoofers and mids as well. But they aren't near as good as the Illuminators.
