So what is the fuss about learning all the keys?
I don't understand the fuss...If you can play a song well in a certain key...
...for some its easy to transpose notes/chords in their mind, but if that is difficult for you, when learning...
1. write down the notes/chords you play in the key you are comfortable
2. tranpose the notes/chords on paper to the key you are trying to learn (you can count half-step/whole steps - whatever works best for you)
3. Play what you wrote in the key you want to become familiar with.
If you do this for a songs you play well in a key you are comfortable with, eventually you will become comfortable in the new key, it's just your mind and fingers adjusting to the movement (for the most part...the chords will be the same) in the new key and thats a matter of repetition.
I find it difficult to use a transpose button on a keyboard, it would be a rare occassion if I ever used it, maybe because I learned on piano. Maybe the only case I would use it, is if I was truly uncomfortable with playing a song I was unfamiliar with in a certain key, but come to think of it, even then I would try to just play in that key...by the time I figured out where the tranpose button is, the song would probably be over...lol!
IMHO...musician that use it, are musicians, they just have not fully learned their craft...Don't rely on the transpose button, you may not have one always...