The word "paintbrush" was cruelly abused by Microsoft (see "innovation" for similiar effect.) If real paintbrushes were alive, they would be suing Microsoft for being associated with "crappy graphics", because real paintbrushes can, as indicated, be used to create masterpieces! So quit spewing those nasty words around, paintbrushes have a reputation to uphold. Many great works of art would not have been possible without them =)
Paintbrush (the program) was originally a DOS program written by ZSoft; Microsoft bought it from them. And, um, kept it fairly unchanged between Windows 3.0 and 3.1, and gave only minor feature enhancements in Windows 95 and 98 (I wonder if the greatest enhancement was the change of name to "Paint"...) It was not a bad PC graphics program when it came out; just that feature-wise, it's still stuck in early 1990s...
Microsoft called GIMP, the popular UNIX graphics package, as good as Paint in the Halloween Documents. Of course, this assumption is absurd; even the most rabid MS fanatics say GIMP is at least as good as Paint Shop Pro. But the bottom line is same - Linux comes with a less antiquated graphics program...