I think they're higher on folders as the bikes are ergonomically designed to be as many things as they can be and to fit a large gamut of differently sized riders.
Most mid-range folders are designed with the idea of them being used for short to mid range journeys across towns for more casual use than a 'sport' machine, so an assumption for comfort (and wearing everday attire) seems to be made making higher bars the choice for a comfortable, less exerting upright riding position.
If you look at any full-size bike with a similar design remit guiding it's function, (3 speed commuters, some of the 'navigator' style hybrids), you'll likely find they too have high bars on an adjustable stem, and perhaps also a shorter seat-to-bar distance than touring or sport machines.
Why they're so high on the Dahon Speed Pro? Well that's a mystery
