Oh, yeah, without a doubt the size tag makes a difference. Logically, I know it shouldn't. I look the same regardless of what the tag says, but psychologically, it's huge. Case in point:
A few years ago, I had lost some weight (which of course, I later found again), but at the time, I was tiny. I could regularly fit in a 4 or occasionally a 2 in US ladies sizes. Well, one day, I was browsing on lunch break, didn't really need anything, and I saw some funky jeans. I tried on the 6, the 4, and the 2. All were too big. I finally found a "0", and it fit! I had to have them, not because they were such wonderful jeans, but because they were the only size 0 I knew I would ever fit in.
Now they sit in my closet, mocking me...LOL!
--Maria