I think the point is he didn't have to make it Sterling or no Sterling. If you stand back and look at the team selection and formation, it mirrored the worst of last season when we now have other options, so the I ask the question; why?
As soon as we went to one striker we improved and as soon as Nasri was played in his most effective position we dominated the match from there on in. 442 with Yaya as one of the central 2 and Nasri as a left sided attacker didn't work for us last season, so why would Pellegrini think anything would change this season? Its just the definition of insanity.
Today's selection was reminiscent of us beating Newcastle (I think) at home playing 442 and Pellegrini using the same formation 4 days later against Barca with Milner and Fernando as the midfield two and thinking we'd get the same result. We were struggling to break down a resolute Watford at home, so we switch formation in the 2nd half and quickly get the opener and go on to win the game, so what happens in the next match? Pellegrini thinks 442 is back on as Plan A against the league's 2nd best team away! This is why I have a distrust of his tactical nous and he just keeps on reinforcing it.