How are people this socially inept? Use. Your. Words. Yes, you shouldn't have to ask people to pay attention, but what good does your silent outrage do compared to saying "Hey, can you move so I can use that machine?"
Gotta agree with #1 here. All you really have to do is stroll by and give a half-hearted "hey man, you still using this machine?" Ninety-percent of the time people will just get out of your way but if you don't say anything then you shouldn't expect complete strangers to jump at your heels and inquire on what's wrong.