It may be down month to month but only due to MW3 being more front-loaded. MW3 currently is LTD bigger than Black Ops
That's my point though, a year from now that will likely not be the case. In any event even if MW3 isn't ultimately a downward trend, I think the popular consensus is that CoD fatigue is going to set in much sooner rather than later, so even if sales aren't down yet Activision would be smart to thinking that far out (2013/14) because it's going to happen at some point. Regardless of sales I honestly think MW3 was the tipping point; IW was a shell of it's former self and it shows, every single person I know who I would dead-on describe as a casual gamer who played the shit out of MW2/Blops for that full cycle dropped MW3 within a couple of months and hasn't picked it back up. In either case though Activision only having to spend the resources on one CoD team instead of two is probably a win for them regardless.