I think you're right. Using your example, if a song is written in G, and i need to play 2 tones sharp in B for whatever reason, the 1/4/5 in B is B, E, F#. F# is a barre chord, and for me B is a stretch. And the 2/3/6 in this key are all sharps, (C#,D#,G#) which will be barre chords most likely. B right off the bat for this beginner is a no-go. It's alot easier to capo 2 tones, rather than learn complex fingerings.
2 or 2 1/2 tones with a capo may indicate the player's lack of knowledge on the complex fingerings, especially in those sharp keys. Of course, if the band leader tells you "2 tones sharp", and you learned the tune in a certain key, you may not have a choice, unless you really know the fretboard and can shift on the fly.