That's because there is probably a free equivalent that works much better.
Adobe photoshop - the GIMP
Word - Latex
Excel - gnumeric
MSN Messenger - Gaim
Outlook Express - Pine, Kmail, ...
I only chose the above since they are the more popular Windows applications. Most of the above applications are available for Windows, but work more efficiently under a Linux distro. Why pay when it's free?
GIMP is a fine web graphics program, but it doesn't compare to Photoshop at all from a production standpoint. As for the others, Office has a market presence that is unbeatable at this time.
Sorry, but the GIMP doesn't compare to Photoshop--no way, no how. The interface is weird and the GIMP doesn't correctly read PS 8.0 CS files.