I don't adjust for any of them. I picked those keys because I can sing those songs easiest in those keys. I probably couldn't sing Jailhouse Rock in A or Johnny B Goode in C. When deciding, if I can't sing in the original key, I move around until I find a key I can sing it in. It doesn't always end up in the same key. It varies widely depending on the song.
I'm having a hard time imagining a singer that wanted to sing every song in the same key.
I'll try one more time. In the short of it - I don't disagree with you. Song styles work best in different keys, absolutely no disagreement at all. And a singer in only one key? heaven forbid that I'd have to endure that (although I know a couple people that come close - and they shouldn't be singing).
It doesn't change the fact that your voice has a natural key that it is most comfortable in. Call it your 'center of voice balance'. Your talking voice is most likely in your natural key.
To answer the question of: What key do you sing in?
I sing in C, but am comfortable in G, D, and E depending on the song. Much lower is no good for me, E is a stretch, higher and cats become envious.
If you answer, I can sing in any key you want. Then you dodged the question or don't really know. No one can sing in 'any key' it's impossible.