The elbows, under current MMA regulations followed by the U.F.C., were at best marginally legal. The U.F.C. clearly states that downward elbow strikes along with rabbit punches are not a legal action. Considering that Silva delivered downward elbow strikes on or around the back of the head would make them technically ilegal (under 2 separate regulations). Don't get me wrong, I don't think Silva should be DQ'd from the fight (I personally don't think downward elbows should be ilegal), but they were definitely borderline given the current rule set. In the post fight interview Lutter even goes on to say that it wasn't the elbows that forced him to tap, it was the triangle. The elbows were just the icing on the cake.
As far as the weight loss goes (according to Travis in his post fight interview), he said that he was to the point where he was not losing any more water weight. With only an hour and a half to go he had to lose 2 and a half pounds.
Now I've never had to cut weight, so I don't know all the technical aspects. But unless someone calls BS, I would take it as a valid excuse. Albeit poor preparation and execution on Travis's part, but valid.