Make a living from playing the verse to 'One Note Samba', and you could use a one note keyboard, too!
Look, I've got a Yamaha KX5. It's a GREAT keyboard, and I play it out a LOT (hooked to a Roland M GS-64). It's my favorite axe to go and sit in with other bands. Takes up NO room on stage, is VERY expressive (there are things you can do only with a pitch strip that are unbelievably authentic), and the short range actually stops me from playing too much (always a good thing when you sit in!) while I have fun being able to actually MOVE around the stage and interact with the band or the crowd.
I have also done band gigs on it exclusively (a casino where there was NO room for a keyboard of ANY size!) for several months. Having a GREAT guitar player is a definite plus when this occurs
So, as you can see, using a smaller keyboard than a 76 is no problem. BUT... Why restrict yourself if you don't HAVE to?
Look, I've got an easy test for all you out there. Take a towel, and cover up the top two octaves of your arranger. How long can you happily play, without pulling it off the keys? Go do a gig like that. You know you COULD do it, don't you? But do you WANT to?
Well, those of us with 76's feel the same way about 61's. I know I COULD use one (I've used much smaller, under the right circumstances). But I don't want to for regular gigs, any more than you all want to play with a towel over the top two octaves...