Very well said...I totally agree with this.
Of course people shouldn't judge others by what they wear, but unfortunately that's just the way society works. Other's first impressions of you *do* play a role in your career and in other things in life. You may be the smartest, most experienced candidate for a job, but then you end up not being selected for it, simply because you wore jeans & a T shirt to the interview, instead of a suit. is that fair? no, but that's how things are. the same goes for this situation..i'm sure others (students & professors) could start getting the wrong idea when they see a student carrying around handbags that cost an entire semester's stipend. they may make assumptions that the student gets outside money (from parents, etc) and therefore doesn't need further financial assistance (and take away scholarship $$). or a professor may wonder why she's in grad school if she can already afford such luxurious items, and therfore infer that she's not serious about her studies (i'm not saying this is right assumption, i'm just saying this is what some profs may think).
this reminds me of a similar thread (i think it was in the LV forum) where someone was worried about carrying a very expensive handbag to their new job. they were worried because they were starting out at an entry-level position and they did not want to "show anyone up" (e.g. the big bosses) by carrying around a expensive designer bag, right after starting the job. some people replied with "you should wear whatever you want, don't care what others think". well i wish it were that simple. it's not completely unbelievable if some senior managers in the company noticed it and got the wrong impression (e.g. she must be daddy's little girl, not very serious about her career, etc) and thus would pass her up for a promotion later on down the line.
so i agree with what India said about waiting a bit until your academic career is more established and/or the profs/students know you a bit more.
I don't know about not getting your job because you wear T-shirts and jeans to the interview; to me it's not that surprising that that will happen. I think it's perfectly legitimate and it shows that a worker or potential worker is serious in her job if she dresses professionally. It's the same as if I were to go on a stage as a classical music performer wearing that same T-shirt and jeans. That's not discrimination; it's something that's simply not acceptable given the settings. Now if you are not offered the job because you wore a birkin to the interview that would be different.