I think it also depends on how much you value the work experience vs. the money at this point. I interned with a small company where I got paid just enough to pay my bills, but eventually that work experience helped me find an awesome full-time job.
Don't get me wrong, I do value the experience and I'm very happy that I had the opportunity to do an internship. But just the fact that the next guy is getting so much more for no reason is very disheartening and making me feel undervalued.
I'm not sure if I have a complete understanding of your situation, but you mentioned the other guy isn't local. Perhaps the extra $8 going towards that guy's incremental expenses because he doesn't have a regular place to live, cook etc. like you do? As far as issue related to pay inequity goes, it's a bitter truth that you'll find it almost everywhere (at some level or the other). It's not a big surprise why HR folks ask you to keep your pay confidential. :) I think sometimes it's not a question of what others are getting, but it's more of am I getting what was was mutually agreed upon? If you think you deserve more, better have a strong justification for it rather than just saying my peers are getting more that I am. You always have the option of finding another different job if you don't like it.