I don't think there is conclusive data that indicates tubulars get more flats.
I think it is mental attitude and the fear of having to repair a tubie flat.
Clement Flat_02 on Flickr
I had problems with a rear clincher for nearly a week of commuting. One trip required pumping the tire up every 1.5 miles or so because I didn't have any alternative. Never figured out why. started using rim plugs
Velocity Rim Plug for 8mm Spoke Holes (Bag of 72) 9332151006534 | eBay