When you read that list of control panel products, and ask for feedback, mostly you just get people leap on page and vote for the one they currently use. Actually, I find them all easy and simple to manage. However, one fact needs to be said, non of them are magic tools and non of them are intrinsically very simple to understand, but if you give some time to learn all of them, then you can produce fine results flawlessly.
Mostly, people choose or recommend cPanel because of its simple user interface, but it doesn't sounds that other control panels aren't user friendly. People usually forget to recognize that a user friendly control panel first requires a friendly user.
I haven't seen a case where customer switched from cPanel, but one thing I can surely say, that every control panel has its own limitations so how could it be possible that cPanel is an exceptional case.
I think, as a web host our job is to understand customers actual needs, and understand what each of them want to use. We can suggest them the right solution, but it all depends on their personal choice.