Good point, but with two caveats:
1st Caveat: I know stepper motors can have their speed smoothly varied with relative ease. Can servomotors' speed be varied similarly? My only experience with servos comes from RC hobby use, and in that context, servos move to the final position quite rapidly, and tend to "twitch" slightly if moved slower (say, by very slowly moving the control stick on your RC transmitter). This minor twitching isn't a big deal for an RC plane's ailerons, but with a camera that needs extremely smooth motion, it could pose a problem. Is there a reasonable way around this issue?