I find that without the horizontal wires, it is easy for the foundation to belly to one side or the other. if this happens, it not only mess up that frame, but also the two adjacent frames (one will be overdrawn and the other will be underdrawn).
The only time I experienced this was using frames that were no square, or using foundation that was slightly oversize. I got some bowing on one sheet, and checked the rest of the sheets and they were all slightly too wide. Even with horizontal wires this would have not corrected the problem. I found slicing a millimeter or two (whats that in imperial - 1/12th inch? something like that) of the edge at the sides helped reduce this "rippling" altogether. I often do this on all foundation now, just to make sure it is not pushed and causing the ripple.
Out of interest, if you look closely at a fully drawn worker comb, the queen will rarely lay in a cell which has the wire running through the base, You can see clear "zig-zag" lines through the comb, often with pollen in as she rejects these cells for brood. This is a reason to minimise the amount of wires through the comb. Although it doesn't look any different to us, the queen is very selective about the cells she will lay in, and often rejects cells for things too subtle for us to see. So you might get straighter comb, but it won't be so effectively utilised.
You are correct we use "W" wires in our foundation.