I'll put my personal biases on the table -- in 1973 my wife's brother gave me an old Avanti track bike as a wedding present. I found fixed gear was just not my thing. Likewise, my first bicycle was a Schwinn 2-speed, and six months later I received a 10-speed for Christmas, and there was no going back. Single speed, even two-speed, was not my thing. I like gears, and I like having at least 12 for a road bike, at least 18 for a touring or mountain bike.

I would think anyone with orthopedic problems of any kind would benefit immensely from a good selection of gears, particularly in the low-to-mid ranges. (I agree that super-high gears are pointless -- top gears on my four road bikes range from 92 to 98 gear-inches, and I really like a 94 (49/14) or a 96 (50/14 or 46/13) top.