Talking about an OLD OS!
I thought XP was supposed to getting old!
An os is not old if it still gets the job done.
for most users, going from XP to vista or windows 7 adds nothing new for them as they are still doing the exact same thing.
The wheel can be considered old but we still use it because it gets the job done.
Other than new versions of direct x, the new OS offer nothing new to to most computer users. but the new OS do use more resources and thus less resources for applications to use and thus a slower OS.
Most people use the OS to run the applications they use. The goal of the OS is to run your programs and get out of the way as much as possible. A good OS is something that allows you to easily launch your programs as quickly and efficiently as possible, and thus the OS should use a little resources as possible.
Other than an embedded OS which is designed to do a specific thing, the OS that most users normally, is not used to replace the need for additional applications.