The reason he takes the LM off first, more often than not, is because his tactics are so rigid and inflexible as are his tactics. He's unlikely to take off Torres, Gerrard or Kuyt and taking off Lucas or Mascherano would mean changing formation or bringing on a CM/DM and that's Spearing or Aquilani. So that only really leaves the LM, probably why he also takes off the LB as often as he does. Any change to the defence would be unusual for any manager unless one player was having a shocker. So we are a predictable, one tactic team and most sides can set themselves up to counter his tic-tacs and exploit weaknesses.
That said, what substitutions are there he can make that can change the match? Assuming Benayoun starts, are the likes of Riera, Babel, N'Gog, El Zhar and Spearing going to change the game? It is doubtful he'd bring on Aquilani, probably not give him more than 20 mins anyway, so could he change it and wouldn't (most) people like to see him on at the start and Lucas on the bench? Kuyt gets a lot of stick but scores useful goals and sets them up too, maybe not that much but as much as players like Benayoun who don't get stick. He's just one player who gets constant stick when the side plays badly, those criticising him making out he is the cause of our problems when last season he was key in our success and there are, believe it or not, (usually) TEN other players on the pitch and I don't see them contributing much most games. We haven't failed to score more than one goal in cup games this season because of Kuyt, it's about time a few stopped blaming him and Lucas and started realising the rest of the team has as much if not more to answer for (as supposedly better players, they should be performing much better more often)