Why do table borders in a PDF look like they don't align properly?

I've noticed this behavior in a few different PDFs created by a few different programs (including InDesign).

This only occurs when zoomed out. When you zoom in, the border looks correct. It looks correct when printed as well, so it's really just a display issue.

What causes this? Is it something about PDFs in general or is it specific to Acrobat? Is there a way to prevent this from happening?