Rhino does do STL Brian... But if you're using STL, then a poly mesh is no problem, and that's 0 problem for me to model...
It's just that modelling with poly's isn't as accurate as Nurbs. Ok, qualifying that... if I model with poly's and follow a profile then all I have to do is ensure that i'm zoomed in to about 1:10000 and it's going to be fine. With Nurbs you don't need to worry at all. A 0.1mm radius will be a 0.1 mm radius because you told it to be so. That said, Nurbs are more of a pain to model with because they can only do certain things, which means you have to model in certain ways to get around these limitations. But with Poly's you don't have so many issues.
What you need to do to Nurbs to get them to be poly's is to tessellate them, which brings it's own set of fun and games. So sometimes it's easier to start in Poly's. Where poly's can sometimes struggle is doing curved modelling on curved surfaces. There's ways around it, but it's horses for courses. But for 99% of the time we jump straight into poly's.
I could probably knock up the above pretty quickly, with little radii on the edges... just if you get stuck.