So, can you run your Vista box without a mechanical hard drive? My A1200 can.
Sure. Just get one of those IDE flashdisks, for example. Also most new systems can boot from USB flashdrives aswell. But honestly, I can't see why ANYONE would want to do "just becouse I can", of course there are some sensible reasons aswell.
Also I can't see why you have "Vista" in that sentence, when talking about features of computer hardware (being able to boot from non-mechanical drive), operating system is highly irrelevant. Just pick one you like. On X86 it could be Vista (as you said), almost any Linux distro, AROS, QNX or whatever, the list goes on... Way beyond "just Vista"