I haven't been playing long, but I am able to play along with some of the simpler songs...

Is there a reason that some artists don't always tune to the correct pitch of in a song that uses basic EADGBE tuning?

Example, I was playing a Robert Plant song, and I tune a string to match the pitch I hear in the song, then I tune the rest of the strings to that first string.

Then I switched to an Eagles song, which also uses standard tuning, but it was very noticeably sharp. Don Henley can belt the notes even in old age, so i ruled out the possibility of them tuning a half step down for vocal range. Does anyone else know about this?

Do lots of people just pick up the guitar tune the strings so they are in tune with each other and then tune the other instruments in the band to that pitch?
I dont think Ive ever played a song with wierd tuning... Apparantly Ive been living under a rock...