In response to the original post: I currently own a copy of many of the CDs mentioned in your post and had them before the 2006 Tony awards. Heck, I even shelled out the cash for two copies of DRS after "losing one" (which I later found in my car).
Why did I purchase them? For me, a cast recording is a way to bring a part of theatre to you. Living in Ohio, I don't get a chance to head to NYC when a show looks appealing to me. However, it is possible for me to hop onto amazon.com and order the OCR. Since I keep up on Broadway shows, I like to be able to know what people are talking about and a OCR is a great way for me to bring Broadway to me.
I'll admit, as a college student with a very little disposable income, it's nearly impossible to purchase every CD I want. I don't download, but I do have a few CDs that I got from my local library (I try to keep these to the out-of-print OCRs and they can order them in for me) I've done some searching at local record stores that sell used CDs. One trip yeilded "Sunday In The Park With George" and "Martin Guerre" for the bargain price of thirteen dollars total. I recently found "Crazy For You" for a dollar in great condition.
Needless to say, I don't contribute as much as I would like to. However, if I have the extra money, I buy a OCR in a case, with the liner notes and photos. After all, supporting a show you love and getting to have piece of that show at your fingertips is what it's all about, right?
"A bird doesn't sing because it has an answer, it sings because it has a song." -- Maya Angelou