I upgraded from a small variable-speed minilathe to a midi about a year ago, and as part of that exercise, I did a pretty careful comparison of some of the options. I don't claim that my comparison was exhaustive, but it was pretty complete.
Bottom line - of the six lathes that I looked at, there was only one that offered ONLY belt adjustments. But of the five that offered variable speed, in every case that option was in conjunction with a choice between at least two belt pulley positions. In fact, one of the things I looked at was where the belt access was - front or side access was OK for me, but access at the back of the lathe would be a PITA because of how lathe would be placed in my shop.
So the choice really is between a belt-only adjustment, and a combination of belt and variable speed.
That said, I agree with Dan - it is really convenient to be able to reach over to twist a knob to go from low-end drilling speed to high-end turning speed. I find that I leave my lathe belt on the low range (200-1900r/min) most of the time. Obviously, the process is different on different lathes - with mine, it takes about a minute, which isn't really a big inconvenience. Even so, I find myself using the machine primarily on the low range - and that's a reflection on the kind of work that I do. If I were a production pen maker, I'm sure I would be using the high range a lot more.