I think the skirt is an acceptable compromise, especially where the 'gap' is barely noticable on the prototype. The pics above at wirksworth are pretty much extreme close up, for most of us the equivalent of the model on your palm held as close to your face as you can maintain focus.
Hattons are probably damned if they do damned if they don't. Compromise the other way, less weight and a smaller (dare we say coreless) motor, no room for sound, non standard dcc socket but a more defined void under the boiler, then we will have complaints that the model is 'gutless' 'designed for collectors' etc.etc.