I assume you mean you'd put $100 down on Houston to cover.
Part of this has to do with gambling tendencies. After the 14th game, the Pats were 11-3 vs. the spread. Mookie pointed out that the only other better bet was betting against Cleveland, who were 2-12 vs. the spread. I'm pretty sure the Pats covered the spread in the last two games, and Cleveland won a game, so betting the Pats to cover was the best bet in the NFL this season.
Vegas sets the spread mainly to get an approximately equal amount bet on both teams. So the spread's going to be higher in the Houston game to adjust for people who bet on the Pats to cover regardless of what the spread is.