Here's the thing - when you throw around words like "unlimited", "abuse" gets really hard to define. Some guy hosting his warez collection for all his scene friends? Obviously abuse.

Me uploading my >1TB music/video collection for backup purposes that will only ever be touched by me? I honestly don't know, and knowing the way accounts are integrated, I'd rather not find out the hard way.

Logically, the acceptable amount they "want" you to store is obviously north of 5GB, since you get that for free by being a Prime member and you're paying for an upgrade, but I want to know where the line is, instead of playing this "it doesn't exist (but actually does and you're dead if you cross it)" charade.

It's much like companies having "unlimited vacation", where the net effect is that nobody takes any due to uncertainty.

How does my taking a company's advertising at its word and treating the unlimited service they provide as unlimited make me an asshole?

The real problem is these companies want to eat their cake and have it too. They want to be able to advertise as unlimited, but not actually provide unlimited.