The traditional American Woman's frame with two parallel downtubes and no effective top tube is very flexible and unsuited to carrying heavy loads. Whatever strength it has comes from heavy wall tubing so it will be very heavy and very few if any came with good components or suitable gearing.
The "parallel top/down tube frame" for women's bikes are not exclusive to US bikes, as there were many British bikes that had the same design, and European countries had some variation on the theme.
Speaking of "Step-Thru Frame Touring", back in June I ran into a German woman touring the Pacific Coast with her very Euro step-thru frame bike.
If I were to look for a step-thru style frame, I'd definitely go for a mixte frame.