The only thing ignorant here is the inability to UNDERSTAND the difference. Your analogy was farfetched when comparing Mac and PC....
1) Newer Macintosh operating systems, such as the Mac OS X, is built on the Unix kernel, which is one of the oldest and most secure operating systems available.
2) Microsoft Windows is used by a lot more users. Because more users use Microsoft Windows, it is a lot better of a target than Apple Macintosh computers.
3) Most of the virus writers are familiar with the IBM platform and Microsoft Windows, and therefore are only going to be able to create a virus for that platform.