Recently been thinking about this and will actually be trying to acquire CDs going forward. I do collect vinyl, but the reason for getting CDs is not wholly a function of wanting to collect physical media. First, there's the issue of sound quality; you can choose what quality you want to put on your iPod, for example, when you import a CD rather than when buying MP3s. You can change this at any time you want as well, if, say, you really get into an artist and want their discography in a lossless format.
Another point that I didn't realize, and I don't think most people think about that much, until recently, is the idea of "ownership" of your music. The licensing agreements for most downloads (iTunes store, Amazon.com, etc.,) pretty much indicate that you do not "own" the music you are buying, just licensing it from them, and that you are the only person who may access that music on a portable device, such as an iPod. Now, there isn't really a reason to care that much about this in day to day life, but it does raise the interesting question of what happens to your music collection when you die (as exemplified by the (false) reports that Bruce Willis was suing Apple over this very issue). It is very much up in the air and the companies could conceivably prevent you from giving your digital music collection to a relative or friend. When you buy physical media, such as CDs, you don't have this problem. For all intents and purposes, you own the copy of the material you purchased and can do whatever you want with it, including re-selling it or giving it to someone else. I don't know about you, but when I pay for something, especially something as personal to me as music, I want to know that I actually own it and be able to do with it what I want.
Kind of a different perspective than I have considered it in the past. Here's a couple interesting articles on the subject for those who are curious:
First Sale Doctrine
Who Owns Your Downloaded Music After You Die?