I don't understand why the popup had to change. The old one was much nicer-looking and less obtrusive (the new one sometimes overlays the vendor window). Also, the new popup shows the cost with no faction discount, no matter which vendor you are at (not sure about the old one). I also like that the old popup gave you the option to repair equipped and inventory seperately (so you don't have to repair items that you're just going to disenchant or sell).
Hehe - I guess there should be an option to let people enable/disable the popup; although, I did find it kinda annoying - had to "X" out of the popup in order to see what's in my inventory to be vendored.