Agreed any idiot can wear a tie, they're more interested in you than what your wearing! Maybe avoid flip-flops though!
That doesn't happen in the real world. Otherwise why does anyone ever wear anything but a burlap sack? And the company doesn't know you well enough to care about "you". You're there to make them want to know you. You're not at the plate ready to show them your stuff; you're still on deck hoping they'll let you play.
I'm not saying a tie is appropriate for an Apple Store job, because I don't think it is, unless you're going for store manager or something. However, while it would be nice to think they were interested in the "real you" and not what you're wearing, an interview is like a blind date; impressions do count. You're trying to bed this interviewer, metaphorically speaking. Particularly when there are many people after the same job, some of whom are probably as qualified as each other. It also speaks to your ability to present yourself, represent the company, and to simply give a damn. If you don't care enough to clean yourself up in order to
convince someone to give you money, how do they know you'll give a crap about the random lady having problems with her MacBook? The important thing is to show you made the
effort. Because the first person who will be crossed off my list is the stoner douche with the guacamole on his neck, qualifications or no qualifications. For the same reason you don't submit your application on the back of the envelope that your Victoria's Secret catalogue arrived in. And I mean, come on - it's one day, a couple of hours tops. Suck it up and be a man.