I guess I should apologize to any members of this list who are or were drummers. I wasn't referring to any of you! I thought you would be used to this treatment - most of the best drummer jokes I know were told to me by drummers ("How do you get a drummer to slow down - put music in front of him!"). I do agree with the point that several posters have made that the skills involved in being a drummer are likely quite different from those involved in other instruments - which may be one reason why drummers who are also lead singers are relatively rare.
But in response to what a previous poster wrote, if a singer can't get all the words of a song out in time, you don't change the tempo of the song midstream (which sounds terrible) - you get a new singer.
Which reminds of another joke: how do you know if a singer's at your door?
They don't know when to come in and they can't find the key.