Why Windows needs reboot a lot more than Linux?

I use both Ubuntu and Windows XP. One thing that catches my attention for a long time is the high need for reboots in Windows. Most of the time when I install a program, Windows requests to reboot system. This happens considerably more frequently than Linux.

Why is it so?

Thanks!

This is because of the architecture.

The major reason for this behavior is that Linux doesn't lock executed files and libraries, which allows direct replacement of those files and does only require the applications to restart. For installations is the reason the package-management-systems, while in Windows every program installs all needed libraries (even if they're already installed, but when they are in use they are locked, which needs a restart to clear the situation) in Linux an application only references the needed packages which are installed once (and never again), reducing the overhead.