Aside from parallel printers and serial ports (which even some PCs don’t have any more), what hardware requirement can an XP PC meet that a Mac running XP natively can’t?
1. 2-button mouse on the top surface. (But see next answer to Cedardave, coming up...)
2. Look and feel of PC hardware. Some folks prefer a Fujitsu, or Dell, or whatever.
3. Screen aspect ratio. Macs tend to be wide and not as tall.
4. More choices of hard drive, ethernet chip, other built-in options.
5. Some people (god help 'em) want a PC because they think Mac hardware looks gay.