The weird thing about the lower number of theatres is that is seems like there's a higher number of tickets being sold per theatre than there were earlier in the month - so people are actually still going to see MMW in places where it's still playing. So maybe Slackbot's experience is a common one in the admittedly-reduced number of theatres across North America that are still running it.
I hope Disney will pick up on that and run it as long as they can. Frozen, The Lego Movie and The Nut Job (THE FREAKIN' NUT JOB!!!) are still running in a handful of theatres even though all but Lego are on DVD/Blu-Ray - I see no reason MMW couldn't do that as well.
At this stage, every weekend it's still in theatres is a victory for me. (I'm recalling that TMTM was in and out of theatres in my part of Canada after four weeks in 1984. By contrast, Ghostbusters ran for five months.)
Side note: The competition took an interesting shift this week with Heaven Is For Real coming out - combined with God's Not Dead and Noah (admittedly a secular retelling of the story), that's a whole lot of Christian content in theatres right before - and after - Easter. With all due respect to the Muppets, I have to admit that kind of trend makes me happy.