wheel - 8:06 pm on Nov 22, 2010 (gmt 0)
ubuntu is just a very very popular desktop distribution. I don't use it myself (I'm on mandriva), but most users rave about it.
No reason you couldn't use ubuntu on both. Or redhat on both.
Remember, linux is linux. There's not a huge difference between the distributions. Gui's might be a bit different. Updating process a bit different. Location of files a bit different. But overall operation, they're pretty similiar.
I use mandriva for everything for personal reasons, but there's no problem jumping on to a redhat server and working on it. The differences between distributions are a lot less noticeable than differences between windows OS's. Mysql is mysql, apache is apache, the kernel is the kernal and daemons are daemons no matter what the distribution.