I was thinking about the same, while working on an article about this subject for my blog sometime ago.
There are several things to consider when it comes to choosing an UI or a personal UI style.
First of all, people who play only one class (not counting occasional low lvl twinks) can concentrate more on ONE specific style, for obvious reasons.
It also comes down how you play your class, even though I don't like that kind of playstyle myself, some people only do ONE thing with their class (like tanking). Even though the class might be capable of dealing damage and maybe even healing, too. Which will also result in a different choice of addons/layout.
Than there is a difference in roles for different classes, even if they have the same role. Like a resto druid needs at least some sort of HoT tracking while a paladin could easily live without any kind of buff tracking (Sacred Shield and Beacon of Light aren't hard to keep track of without an addon).
After all the role of your class defines the most of your interface decisions. For example, a DD could get away without any raidframes, at all.
I personally try to always create an interface that - AT LEAST - is capable of fitting all roles my character can choose from. Since I play a paladin since vanilla, I can use my UI for pretty much any other class/role, too. Which I consider a very good reason to handle it that way.
If you care to get rid of unneeded information and if you choose a good layout during the creation of an interface, you won't end up with a complete mess, even if you change your role or class, later on.
And finally, a good interface is NOT dependent on class/role/whatever. It's only dependent on how capable someone is to get things done right (functional, clean, at least somehow pleasing to the eye). And that is achievable for everyone, by following simple design basics.
