Well, no kidding...You don't suppose it has anything to do with the fact that hackers/crackers aim for MAXIMUM effect and Word, Outlook and Outlook Express are the most widely used word processing program and email programs in use all across the planet do you???
If anything else ever takes the mantle, the hackers/crackers will change gears.
BIND (Berekeley Internet Name Domain), OpenSSH, Apache, and sendmail, the most widely used DNS application, secure shell application, web server application and email server application all run on UNIX systems!
True, but it also has to do with the fact that they immediately trust and in some cases execute code or data downloaded from anywhere, without even asking the user.
Wordperfect, Quattro Pro, the Lotus SmartSuite office package, and OpenOffice do not have these vulnerabilities, period. Netscape Mail, Pegasus, the Bat, etc. do not have these vulnerabilities either.
How do you explain that? HINT: it is a question of bad design vs. good design.