It really depends on the tires contact patch. This will depend on the tire width, wheel width as well as vehicle weight. Wider tires on a narrower wheel will cause the tire to wear like it's over-inflated unless you lower the PSI. The downside is lower pressure means the tire will ride softer and generate more heat which means wear.
When I was running 35x12.5R15's on 15x8.5's I had to run around 25-27psi to get a even contact patch. For my 33x10.5R15's on 15x7's I run 35-40psi. So whoever told you you shouldn't run your tires over 28psi doesn't really know what they're taking about. It's not a one-size fits all sort of thing.