I dont think its a solid piece. heres why:
1. Time/era. Making it (The clamp) out of plastic wont work, its got to be spring to be a compression clamp. That means machined. Not cast. You cant cast spring steel, at least not that I know of.
2. Weight. The weight of the thing would quadruple if the riser was steel. Again, weight = money.
3. Energy transfer. Why make a 1 piece mount? What are you raising away? Your either raising another tubing, or holding the tube away from something, usually for heat reasons. Solid metal would transfer, vibrate, etc. This is the weakest of the four arguments.
4. Mount being solid would stop the spring from flexing at all in almost 50% of the area, causing it to be a lot weaker, because allof the stress would be on the arms, where they thin out in order to overlap/wrap and be sprung. Again, not a good design. The ribs on the mount are to stabilize lateral movement, as well as horizontal. Otherwise it would be a solid piece. Because its 'ribbed' means they were keeping weight, and materials down while adding stability. The 'addition' of stability would difinitively stop it from flexing and defeat the purpose of a 360 spring clamp.
I would bet its a spring steel clamp, with holes in it, and the riser has tabs that fit into each hole. Its not glued, or it wouldnt flex properly. Now, i dont think that they scratch built it. I think its a piece, thats two parts, but probably doesnt come apart without breaking it.
*hammer*
Rebuttle?