In my opinion a long term linux release is only suitable for servers (and in some cases it isn't), for end users is pointless, you have to deal with outdated software. An example is video drivers, they are still evolving and theres no easy way to install new versions without compiling the whole xserver and linux kernel (something that not everybody is willing to do). Another example would be PHP, that in this case it is version 5.3 on squeeze while 5.4 - 5.5 have lots of optimizations (opcache) that would benefit a server performance. Also newer kernels have introduced power usage improvements making a server be more energy efficient.
Windows XP has survived a lot because it is easy to download the installer of latest software versions and have it working on your system in a few steps, while on a linux distro you mostly depend on the main software repositories (outdated) or third party repositories which are a pain to deal when upgrading the whole system.
This LTS releases should adopt a semi rolling release model where new software versions is stability/compatibility tested and rolled out to main repositories when testing is done. Missing the advantages and improvements of newer software versions is a drawback in my opinion. I think LTS is a waste of human resources.