I'm getting scared now ... here's the latest response someone received from htc (this was taken from htc.com support form) ... htc is actually telling people to go find an app in the marketplace to try to make it work!
1st response from HTC: I understand the importance of being able to playback your videos with superior sound. The concern you are experiencing is due to the Noise Cancellation software being enabled while the device is recording. Due to this, the sound that you hear is that from the microphone on the bottom of the device. You could try third party applications from the Android market. I do apologize for any inconvenience taht you may have experienced.
2nd response from HTC: Thank you for your reply. I understand how this can be frustrating for you. I tested this myself, and found similar results. Covering the top microphone improves voice quality on recorded video while covering the bottom microphone improves the background noise. This makes sense with how the noise cancellation software works. This is something that our engineers will have to look into and I will forward this information to them, however at this time, we do not have a fix for the native camera on the device. I do apologize for any inconvenience