Hey Bruce! Yes, discussion is good. Ultimately negotiating with some clients may not be tied to what is best for learning. (That's a whole different discussion unto itself!) One thing you could do if they insist on designing to account for various learning styles is send them over to collect on Wil Thalheimer's Learning Styles Challenge. He's offering $1,000 to anyone can demonstrate that utilizing learning styles improves learning outcomes.
http://www.willatworklearning.com/2009/09/learning-styles-challenge-threeyear-update.html It's been a lot of years and nobody has collected yet.
Although the research is a few years old, I think the findings are still valid. I don' t think that human brains evolve quite that quickly. If you dig into the details a bit, especially the part about dual channel processing I think it makes a pretty compelling case. I'm also very curious to hear what you and others think. I look forward to the discussion. 8-)