I'm kind of guessing though that new, newer, newest, machines will be the ones most likely to be missing support for various bits of hardware. True?
Not sure. Anything with a pure Intel chipset will
just work on Linux, either at release or within 6 months (Ubuntu release cycle).
In the past, Toshiba and Compaq branded machines seem to have given the most difficulties, and Dell and (especially) Lenovo machines generally work without issues (unless one has last week's latest ATI video chips.. but that's apparently also now much better).
Cheers