As r00fus mentioned, I think that's giving Maxthon a little more credit than deserved. The 'core' of IE6 was still IE6, and adding a bunch of fluff around it didn't change that. As such, the IE6 engine, the thing that mattered, went untouched.

That isn't to say that Maxthon wasn't awesome, it was. But it also wasn't nearly as pervasive as even Safari is really.