Surely most people in that kind of situation would move to gmail/hotmail/yahoo or similar, though? I'm sure my ISP offers me a free email, but I can't say I've ever used it (or even asked after it...)

Users using cloud e-mail addresses have addresses that are slightly more stable, but eventually they decode that @hotmail.com looks better than @aol.com, that @yahoo.com looks much better than @hotmail.com, and eventually that @gmail.com looks better than @yahoo.com. When they do this, they change their e-mail addresses, and often just derelict the old one so they don't have to think about it anymore.

Also, to the extent to which this becomes important, it only becomes important too late, as in after you've already used an address or two. I have had the same address now since 1997 when I registered saurik.com, but I did that because I had in the two years prior "learned the hard lesson" that my ISP-provided e-mail address was doomed to be something I'd end up having to move off of, potentially fairly often.