Yes, you buy DVDs, as do I. You missed the more important part of the question though, when did you last watch it on a PC as opposed to just using a DVD player?
Seeing as I don't own a DVD player, only a computer, all the time actually. And that is true for 99% of my peer group (students). One device to rule them all, one device to find them, one device to bring them all and in the darkness bind them - the PC (or Mac).
Microsoft did a special deal with Dolby so that they could pay the license fee for certain codecs in place of the OEM, which was pretty much a necessity so that they could sell Windows in a sane fashion. However that agreement only covered Windows 7 and is invalidated by an upgrade. Remember the license is to "the device" and not the end user, otherwise the fact you own a DVD player could make all this discussion redundant.