You know, I've always been on the fence about this in some games. I think it was a bad idea in Simcity, but I can understand some of the rationale behind Diablo 3.
However, there is a more serious problem with an entire console requiring always online. What happens 10[5] years from now when XBox 40k comes out and they now need new servers to handle that system's always online functionality? Do they lower available bandwidth and make people deal with it? Do they run twice as many servers, doubling the cost of it all and possibly having to squeeze more money out of the consumer for it? And more importantly, what happens 20[10] years from now when they stop producing games for it altogether? Do they shut down the servers? Is there a potential firmware upgrade that will let the system run on its own? Will a single game available on the system be playable in the future? Do they even care if it is?
Obviously these are all pure speculation, but I'm 30 and I still have my original NES which still is in perfect working condition over 20 years from when I got it. I've seen the beginning and end of the PS2. It lived a long and full life, and I still use it because I enjoy games for it. Hell, I've only ever owned one vacuum cleaner, lovingly pushed along many a carpet. There is basically no way they can assuage my fear that any game I play on that system will eventually become obsolete and unplayable. I can't think of any way they can assure us that they would support any kind of way to archive those old games (aside from the obvious re-packaging as download-only on a new system, forcing you to re-buy, since obviously backwards compatibility is a thing of the past). It's a gamble I am not willing to take.
(Here's the vacuum comparison by the way. If there is a possibility that in ten years, you will HAVE to buy a new vacuum cleaner because they no longer support it, would you buy that vacuum?)