Granted, for occasional air travel, a non-folding frame with couplers can certainly make for a smaller package...but there is a considerable difference between a take-apart frame and a true folding bicycle. A Bike Friday can offer a full range of travel choices...plane, train, bus, auto...in only a matter of minutes.
I don't consider a BF's wheelset to be non-standard at all. It's a very common 20"/406 size...easily obtainable in most locales. Also, the drivetrain parts...shifters, brakes, cranks, changers and so forth...are all based on the industry standards. No surprises here.
If I were in the market for a full size tourer and planned to fly once or twice a year, then a coupled frame would make sense, especially from a company like Co-Motion. But, I wouldn't sell short a well-made folder like the Bike Friday.