<< Just my imagination or is there a valid reason for this? >>
There's a perfectly valid reason... the compound(s) used for the brake pads.
Generally speaking, higher performing pads will kick up more dust when you get on them. If you watch any Speedvision Touring car or GT races, you'll notice that you can actually see brake dust fly out from the calipers under severe braking for some cars.
<< I have a 2000 BMW 3 series, and I get squeaks when I brake at low speeds >>
I'm guessing that a lot of Euro cars use carbon-metallic pads (which stop much better than the organic one used in "normal cars") and (not guessing) the higher metallic content is what causes the squeaking. You can possibly remedy the squeaking by changing to a high-performance composite brake pad like Porterfields. They'll spew dust still and put more wear on your rotors. The more metal or high friction composite in the pads, the faster you'll wear your rotors. Full on race compound pads sometimes need to be warmed up, and they can be so "hard" as to destroy your disc rotors. Also, since 80% braking is done by your front brakes, they'll probably have lots more dust...
Those extra long life pads are probably very low friction and won't stop you very well, probably cheaper, and won't wear your rotors that much. Hope this has been informative! 🙂