There are differences, but there is also a norm. For me, the norm is dynamo hub with lights, fenders, and preferably some kind of luggage area. I have bikes that don't have these things, but they don't get ridden as much as those that have them.
Among those that have them, there's some variety in terms of wheel size, handlebar shapes, gearing... but oh, I don't know... maybe they are all the same after all.
And they all ride like bikes, right?