Apart from the fact that is no excuse, it doesn't excuse the fact they do so in European competition as well, nor does it explain how they became so endemic at Chelsea, or how blatantly his Porto side were diving against Celtic in the UEFA Cup final a few years back.
I already covered how Porto's run to the CL final saw them avoid most of the big guns (and when they did face them, they either gave away four points to real, or beat a Man Utd team in dissaray), and the same can be said for Inter: dropped four points to Barca in the group stages and also drew with Dinamo Kiev and Rubin Kazan, beat Chelsea as they were between managers (again) followed by the mighty CSKA Moscow, then parked the bus against Barca in a match they had one shot in 90 minutes. Bayern had tougher opposition throughout the tournament, as Monaco did a few years before.
It should also be noted that, in order to meet Mourinho's "ambitions" in the transfer market (read: meet his budget), they had to do cash + player deals to sign Milito, Motta and Mariga, as well as sell Ibrahimovic for the best part of €50m with Eto'o thrown in (and made a €50m loss on transfer dealings the season before) Once again, this is not a financial arrangement we can operate under, as we don't have £30-40m to write off every summer, nor do we have many players we're willing to send in part-exchange that could knock a chunk off the transfer value of a Premier League player we're looking to sign.
Mourinho's record is as much smoke and mirrors as the chances of Daniel Levy losing his sanity and bringing him in is likely.