If you are still plagued with the HTC Evo 4G graphics performance issue that is capped at 30fps, the recent explanation by HTC media personnel during the meet with AndroidGuys writer at HTC Aria Event may clear your doubt. According to him, it is due to hardware performance limitation and hence the media playback and web surfing are capped to 30fps so that the graphics core bandwidth can be allocated to support HDMI output display without suffering severe display degradation.
The fix is purposely implemented by software to regulate the Snapdragon CPU, so that there is sufficient horsepower ready for HDMI transmission. While it seems to be good enough to cater for small screen smartphone device since most of the video playback are filmed in either 24fps or 30fps but in actual fact, the effect is quite significant especially when running animation screen, doing webpage scrolling or even just some pure basic menu navigation.
Apparently, HTC overemphasized the importance of HDMI feature which may have heavily impact visual experience even on the mobile device itself. And one immediate fix that we could think of is probably having a way to detect the HDMI port usage and eventually lowering its FPS figure when necessary, which is able to be done via OTA (On-the-Air) update.