I don't care where a person buys their clothes or what brands they do or don't wear. But generally if a person goes into a store like that, or any store really, and buys clothes with the store's logo emblazoned obnoxiously across the chest/wherever... It's like an excuse for not developing personal style. It makes me think that people don't know how to make their own style choices independently of what other people think, so they just throw on this shirt with a brand name all over it, because it seems nonthreatening and is widely accepted.
Personally, I'll wear completely plain solid-colored tops before I'll act as a billboard for some big corporate clothing company. The only time I would wear that kind of logo and essentially 'advertise' for a company is if I was really into their products and they were virtually unknown smaller companies. In which case, I WANT them to succeed, and I obviously vouch for their products as far as quality and style go.
I try not to judge, but it generally suggests to me that they're superficial and materialistic. Who cares what the name on the tag of your shirt reads? And if the brand is printed across the clothing for everyone to see, you're just a walking advertisement.
It kind of annoys me a little bit, but then again I do the same thing. I feel like it's different for a girl than a guy. Girls can be materialistic, but it's kinda odd when guys are that way. It kinda shows that they don't really know how to express themselves through their clothing, so they advertise popular brands instead.