Agreed on that - I've ridden (and currently own) both a top tank and a step-through model, and I definitely like the fuel capacity of the top tank. (Plus I find it a bit easier to fill right up to the brim at the gas station, but thats just me probably)
The step-throughs on the other hand tend to get less hassle, people don't see them as a "mini motorbike" and don't bother you if you chain it up to a bike rack as much, or park it off in a corner behind something. (They're much more likely to bug a motorcycle rider that way)
Aside from that, it comes down to preference... both are clearly mopeds by any reasonable definition and both have their advantages/disadvantages. (Depending on design) I like the top tank's general "feel". But aside from the gas capacity issue - its all a matter of what you prefer.