I think you have to consider the situation here. The Bill managed to score on a one play drive, following a Schaub pick, then again after completing one first down, following a big kick return. Outside of that, this offense did absolutely nothing, other than go 3 and out on most drives.
Total time of posession for the Bills? 20:52
The type of production above by an opposing offense is an absolute gift for just about any running back on the opposing team.
More than anything, this was a perfect opportunity for Kubiak to do what he did. It was a game where he could afford to make a statement to Slaton, with little risk of losing the game. What made it better? The Bills continued to do absolutely nothing, so Kubia could easily just keep Slaton on the bench.
Next three games, Texans get the Colts twice, and Tennessee. They can forget about these teams having the ball for only 20 minutes. Houston will need Slaton back on the field, hopefully paying better attention now to holding on to the football.