I'd say there's a difference between expressing yourself through having a great record collection and actually writing music (even if its a really trite song). Creative writing, music, art - even if they rely on conventional forms (language, materials, etc.) is to me different from buying, collecting and arranging a bunch of items designed and made by other people.
That's a good point. Although, of all the things you can buy as a consumer, clothes seem like they're the most personal.
Critiquing clothes, for example, is not at all like critiquing someone's music collection. You can say someone has bad taste in music, but while that's somewhat of a personal attack, it doesn't carry the same weight as saying they have ugly clothes. Even for mainstream, middle-of-the-road brands such as J. Crew, whose customers go there deliberately so they look like everyone else -- those customers think of their clothes as extensions of their personal self. Saying J. Crew is ugly to someone wearing J. Crew is not at all like saying you hate Kanye West to someone playing Kanye West.
I also don't think the standard for self expression should be doing something totally new. Maybe the music thing was a bad analogy, but since clothes are fundamentally social -- ways we communicate our identity -- they have to fall in line somehow with a language that people can understand. Meaning, for self expression to happen in the first place, there's a strong tendency to use stylistic cues and symbols that are common (leather jacket = rugged; tailored clothing = fancy; sneakers = sporty). The idea that something has to be both totally new and self expressive is almost at odds with each other. It would be like trying to communicate something about yourself using a made-up language.