I don't see many EPICs in the store for loose hinges. Maybe once or twice every week or two. However, we tend to sell a lot more EVOs around here. It seems to be the choice in this area.
I usually just tighten the screws. If the customer is happy, I let them go. If they continue to complain and I can't get them satisfied, I've done an exchange before to keep them happy.
I'm not aware of 'new' EPICs with a better hinge. But, it's rare that I see EPICs in the back. Don't recall seeing anything in Sprint tech forums, etc. Seems to me the first batch (or part of the first batch) was plauged with horrible 'buttons' on the bottom. 'Back' in particular. But, don't notice that on new units or the couple refurbs I've ordered.
Sliders in general have this problem. It's just the nature of the beast. More moving parts, more things to screw up, etc.