Hi JL:
Hooded dropouts like these are sometimes referred to as Breezer-style, as Joe Breeze used them in his MTB. (IIRC, they predate Breeze, though.)
Hooded style has advantages for builders and Riv: this one can be used at many different angles. Vertical dropouts, like on my Toyo AHH, have a fixed angle. As the frame size changes, the chain-stay to seat-stay angle needs to change (or the frame designer will have to compromise by changing stay lengths).
Hooded style also can be welded (and brazed, I assume), which might offer flexibility in manufacture. Might permit a cheaper frame-construction option? The width probably offers a stiffness advantage, but I don't know how significant or important that might be.
shoji
arlington ma