Use of a bike is a huge factor in both sizing and adjusting (ie. determining stem size and seatpost position) a bike to "fit". For road bikes, TT length (or more accurately saddle to handlebar length) is more important that ST length. I am riding 4 road bikes that vary in size from 51 to 57 cm (ST C-C) but their TT+stem are within one or two cms. My do it all mule and long distance bike (not included in the above count), has a longer TT

As far as stand-over height goes... I suspect that a lot of men really want to avoid the possibility of an involuntary vasectomy without anesthesia in a hard stop, thus the recommendation for straddling over the TT. And, frankly, it all depends on how experienced a rider is (so he can avoid such an unfortunate close encounter with the top tube.) If you think you are good enough to deal with a close encounter, more power to you, but if you try to size a novice cyclist...