The more I transcribe rock/pop songs, I notice that almost all of them are in the key of E and A. I notice that 99.9% of funk/slap songs are in E or A. Apparently, these are considered guitar keys. Is this because the low open strings can be used for power chords? Why is this exactly? When I am jamming with a group, I tend to assume the tune is in E or A. Do any of you all assume the same thing?