It probably isn't 800 lumens and/or the room wasn't perfectly dark. Depending on how the ambient light gets into the room (or demo booth) can play havoc with an FPTV.
I wouldn't recommend a Grayhawk for that picture size. Grayhawks work well with the big lumen LCD projectors. A 2000 lumen LCD projector is typically very close to 2000 lumens. A 800 lumen DLP usually isn't.
Little known "fact" that the LCD and DLP manufacturers had a Mafia-style sitdown a couple of years ago where they decided that the DLP guys would be aloud to lie about lumens if the LCD got to lie about their contrast ratio.
Now the LCD guys are starting to come a lot closer than the DLP guys are on their lumens. Heads are going to roll (if your eyes aren't already).
This is all conjecture of coarse. The Sharp might be making its lumens output, just being demo'ed in a bad room.
Too dim is always a relative term.
-Mr. Wigggles