HD videos are usually HD in picture only. You'd be amazed at how few camcorders (let alone pocket solid state video recorders) have any kind of line in capability at all. And few demonstration booths at trade shows even offer a direct feed out, for the few that HAVE this capability. Then there is level matching, which again, few camcorders do well except for TOTL broadcast models.

A noisy trade show floor is a difficult place for even the best mikes and camcorders. It's just the nature of crowded rooms and halls, and mikes...

Your best place to stand is right in front of the speakers if you want to get the best audio (but even there, you often have issues of the sound distorting the mike or input electronics) but may not be the best spot to SEE what's going on. It's a tough environment for even a professional videographer to get a good recording, I'm afraid.