A simple comparison of X Window Desktop Environments that is just a little bit of technical info if you are interested in that also available is:
A comparison of X Window Managers which is also quite interesting
Personally I find KDE to be bloated with loads of pre-installed software, and it just ‘feels’ clunky for some reason. I prefer Gnome as it is a bit more lightweight but still has functionality, as for even more lightweight Xfce is nice and I’d love to get into Fluxbox but I find it difficult to get used to.
This provides another comparison of KDE and Gnome using Kubuntu and Ubuntu.
The reason why the desktops look like they are ‘trying’ to mimc OSX/Windows is because it’s a formula that works. Why re-invent the wheel? People are used to that layout/format so why take them to a completely different world when you can ease them in slowly? If every linux distro used Fluxbox as their default window manager a much lower percentage of people would use Linux because it’s more complicated to set up and change and just doesn’t have that ‘familiar’ feel about it. It’s like if you were building a car, why reverse the pedals and the steering just to confuse people? Gnome and KDE are the main default ones that people will find easier to get used to, however with Linux you have the choice of moving things around, changing your window manager, your themes, and lots of other stuff with a little bit of ‘know how’.