I agree with Mike..you just have to practice and loosen up to hit the note....I have sung various style including rock with bands for many years and it is up to the band to cater for the key to suit the singer not the other way around. My band never had a problem changing key if needed.
But hey if you do not ask you do not get...There are some songs where the guitar cannot quite get the right sound or due to the key finger shaping becomes difficult...but they are the exception..only ever come across a few.