On the Three Wise Men CMS system I overcame this by licensing a fabulous Applet based editor from Ephox. I like it so much, I continually try to work it into other projects. The only issue is that it’s expensive (well that’s a relative term, with our CMS product the WYSIWYG editor used to be our largest tech-support call driver!), so you have to have a strong business model behind the web-app. In the end, however, our users have thanked us, over and over again.
Really this is like a lot of technology, when customers don’t know you, they don’t know to trust your judgement. All the experience in the world on your side won’t help if you can’t argue your point convincingly.
So sharpen that saw, try to find ways to explain things your experience has taught you in a way that customers can understand. It’s worth it.