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Seam shaping is old sail tech. You'll only really see it on old one design classes of boat like 470s' and cruisers where there's no battens.
Boat sails, many of which are higher tech than windsurfer sails, normally have seam taper whether fully battened or not. I seem to recall being told that you get wider wind range if you use seam taper as well as mast bend, which is also easier to adjust on boats. I think it's part of the reason that many boat sails have much wider wind range than a modern windsurfer sail.
If it's only battens that force draft into a sail, the sailcloth tries to distort into a different shape between the battens, which is not healthy at all. I don't know the turnover of some windsurfer sail manufacturers but there's a lot of big boat owners who could buy the whole industry with their beer budget; they're not using "old tech" or penny-pinching, but they do have soft sails with seam taper.
As to the original question asked about the manufacturers spin on forward draft , I believe there trying to say the sail pulls from the mast area apposed to from the middle of the sail. As an old school sailer , now new school , I have noticed that sails now pull more from the mast forwardly , that's why we can now ride the board flat , lean forward and push sideways on the fin. Would it be bold of me to say that forward draft is the absolute of what we want if it wasn't for the tradeoff of weight , sail rotation and ease of use ? Before we had to lean back and carve the board. I like modern stuff , 
Ok, after doing a bit of research, yes modern battened sails do use a bit of seam shaping to stabilise the sail. I stand corrected.
Chris, my reference to "old tech" was largely to do with the days of battenless sails when all the 3d shape in a sail came from seam shaping. The amount of seam shaping in a modern sail (windsurf and skiff sails) is barely noticeable compared to a no batten cruiser or one design dinghy sail, such as on a laser/470.
You have just had two highly experienced sail designers tell you unequivocally that all modern sails have significant seam shaping and that it is vital for the good 'tuneability' and stability of the sail.
Some pure Wave sails may have a lot less than Freeride and Race sails, which usually must have a much wider wind range, but if it wasn't there at all the sail would feel like crap as soon as you were fully powered up.
If your sail does not seem to have any seam shape, I suggest you try one that does! 
