Here's a link to more info than anyone probably needs to know regarding Toyota's HSD system.You are showing a traditional CVT. It has a primary shaft with a fixed cone and a sliding cone. The secondary shaft has a fixed cone and a sliding cone. There is a belt between the two shafts. Oil pressure adjusts the position of each cone and that gives you your infinitely variable ratios.
The Prius and CT200h actually are must more similar to a traditional automatic transmission. The main planetary carrier speed is controlled by an electric motor instead of various clutch packs, though. Controlling the speed of the motor controls the planet and ring gear speeds and thus the output shaft speed. I've torn apart both a traditional 6 speed auto and a hybrid CVT. The CVT is impressively simple. It really is brilliant. I'm sure the controls are very complex, but mechanically, it looks like it would have far fewer modes of failure just based on mechanical simplicity.
As far as why the engine doesn't rev over 2500 with the car in park, you are probably right. The ECU logic says "stop wasting gas, dummy" and limits the revs.
Toyota Prius - Power Split Device