I am not trying to justify the decision to take out the closets, but I was looking at the configurations of other airlines, and most planes that other airlines are flying on the same types of routes as the US A320s do not have closets.
AirTran - None on either the 717 or 73G
Alaska - Only plane with a closet is the 739 behind first class. No 734, 737, 738, MD80
American - No closet on MD80s or TWA 757s. Yes on 738 and orginal AA 757s
Continental - No 733, 735, 73G, 738, 739, 753. Only BizFirst 757
Delta - No 738, no on new upgraded 757, no MD88, NO SHUTTLE!. Yes on 763 domestic and MD90
Frontier - No A318 or A319
jetBlue - No A320 or E190
Midwest - No on 717, MD80 premium, or MD80 saver
Northwest - No A319, A320. Yes on DC9-30, DC9-40, DC9-50, 752, and 753
Spirit - No A319, A321
United - No A319, TED A320, No 1 version of 733, no 1 version of 735. Yes A320 (regular), yes both 752 (regular and PS), yes on 1 version of 733, yes on 1 version of 735
United and Northwest seem to be the only carrier that have a relatively large amount of planes with closets. But even United doesn't have them on their A319s, their Ted A320s and some of their 737s do not have them..And they fly a large amount of routes in cold temperatures like DEN, IAD, and ORD.
Northwest does not have any closets on their A320 series aircraft, the largest type in their fleet, even with MSP and DTW megahubs.
American only has them on 738s (which mostly all fly from Miami) and AA 757s. The MD80, by far the largest fleet type does not have them.
Continental basically does not have closets on any domestic plane. And they fly from CLE and EWR
Delta is really lacking with their fleet. No closets on the shuttle. Basically the only domestic plane they have them on is the MD90 which flies almost exclusively out of SLC and Delta has a very small number of that fleet type. The domestic 763s do have closets, but these have begun to be slowly phased out of Delta's fleet, like when they recently sold some to Hawaiian.
While I don't think that US should take out the closets, its not like they are going to be losing much ground to their competitors. It's not a standard to have closets, even with top-tier carriers like CO who have hubs in frigid weather cities.
If you want to b*tch about taking away first class seats, yeah that stinks, go ahead. If you want to b*tch about audio and emergency equipment in the first class storage bins, thats fine too. But the closet issue doesn't seem to be that big of a deal.