It could also just be image advertising for the Acura brand. X% of the annual marketing budget isn't model specific and is designed to keep the brand "top of mind" in the public eye. The MDX has been on the market for a while now and new entrants are popping up and getting press so it's not illogical for Acura to promote it even if there aren't enough to sell. They've been running tons of CL ads (and are offering huge dealer incentives) because there are a lot of 01's and 02's on the lots and Acura just released the '03. They just released a new RL ad featuing OnStar that's been running frequently too - and the RL is definately not selling that well.
Interestingly in the 1 1/2 years of MDX history I have only seen about 6 commercials for it. All have been during sports programs. Never seen one in prime time. Seen pleanty of other Acura commercials in prime time though.
BTW the one that was on last week was the guy going skiing and thinking of reasons why he was sick or missing work?