Telcos have been around for 100 years; they know how to do DC; they do it quite well; you might as well use what they got instead of wasting time fighting for what is 'right'. Its not like its all that hard to get the gear that ISPs use to run off of DC.
I readily agree that if one has no choice one can get 48VDC equipment. The problem, as I see it, is that the overall cost of the facility providing battery backed up AC and people using standard mass produced equipment is substantially lower than the cost of the users all finding oddball power supplies and the facility providing DC. Furthermore, there is the issue of dramatically lowered convenience.
FYI Telehouse Europe in London which hosts LINX (London Internet Neutral Exchange) provides AC power by default (doubtless they will do DC power if you ask). They are both an FM facility for dealing rooms etc., have several colocated telcos, and lots of ISPs. We haven't (to my knowledge) had a single AC power failure since we've been there. They have the entire building UPSed with 2 very large glycol generators and enough fuel to last for at least 3 days. It's possible to do, and it works. And the price is from memory cheaper than MAE-East. Telehouse NY (same people) are also starting an IXP. It will be interesting to see how they compare. Alex Bligh Xara Networks