I think the most notable difference in EQ simply are the curves. And since they are different in most plugins, thats why they seem to sound different. But they aren't really, they just do something else. Because +6dB @ 2kHz with 1.5Q in plugin X might do something completely different than in plugin Y.
The whole saturation and phase-stuff sure is nice and can improve the sound further, but it's certainly not the main reason for the "sound" of an EQ.
That being said, I also have my favorites for special tasks, i.e. the 1973 EQ for hi-boost, rEQ for cutting mud and such, but I'm pretty sure that this is mainly because of the way the EQ-curves are designed and fit the task than any saturation or phase alteration. However, I also tried some EQs that I just could not get to sound like anything I'd ever want
And EQs without graphical display always sound different that the ones with, right?
If I can't get it right with a "normal" EQ, no super special high end EQ will make it awesome.