It looks like HTC has made their first "blunder" of sorts in that the firmware on the HTC EVO locks all 2D and 3D applications at 30fps. The Google Android team however shoots for 60pfs on all handsets and thus, your potential performance has been cut in half despite having the hardware necessary to push the 60fps.
The Nexus One, which has an identical GPU/CPU combination has no such issues reaching 60fps, so the problem is certainly something in the software category.
The Android team is well aware and you can read some of the reports about the issue on both XDA and the Google Code forums at the following links:
Evo capping all graphics to 30FPS:The reason why graphics performance sucks right now - xda-developers
Issue 8942 - android - Sprint/HTC EVO 4G 30FPS cap on 2D (Canvas) and 3D (GL) - Project Hosting on Google Code
FYI - Both GL and Canvas are locked to 30FPS on new phones. - Android Developers | Google Groups