That's an interesting observation, and a question I have wondered about myself. One angle makes it good for savvy players though. It means the progressives are more likely to get to a point where the return on the machine is over 100%.
There's an ever better example of this at
RTG, where the "It's Good to Be Bad" progressive has never hit at either denomination (25c or $1). (At least, since I've been tracking them for a year and a half.)
In that game, it's tough to stay the course and go for the progressive, because you're offered more and more free spins to bail out. I suspect that the 25c version is well over 100% return.