It bothers me. There are too many things that are either not standards-complient or support different parts of the USB feature set that compatibility is a wildcard.

I carry a large backup battery when I travel for work. It can keep my laptop going under load all day, allowing me to not care at all about proximity to outlets when working. It also allows me to painlessly recharge phones by just handing it to someone.

Last week, I was running something from someone else's laptop (enterprise HP, like mine, but different model). It got low, so I pulled out my battery. Plug it in... No power. I could see the voltage fluctuations of it negotiating, but nothing after that.