Not sure how long these have been around, but Tesco and Amazon now both have mp3 download services.
Amazon's is far, far better. But the issue here is the price: it's still TOO EXPENSIVE (unless you're buying really common chart stuff, when it might be cheaper). For most things, it's 79p per track. It doesn't take a genius to work out that if I can buy The Early Years by Roxy Music for £6.98 on CD, or download it as mp3s FOR THE SAME PRICE, I'm going to buy the CD and wait two days for it to arrive. I'd rather have the physical object, thanks very much. How complicated is it to work this out? If the mp3s were around £3, I'd have bought them: immediacy + lower price - transience of medium > possession of the physical object - higher price - 2 days waiting.
Of course, the temptation is always there to skulk around bittorrent sites looking for it. Bear in mind I already own all the tracks on that CD, across all the early Roxy Music albums. I resent having to pay at all: I've already paid once. Don't get me started.