If you were using Portal mode you could simply check a box to output your < table > tags to < div > tags which would be more helpful. Did you take a look at the form controls within the CMSFormControls directory? In some cases you may be able to modify it there (I'd recommend cloning it and not breaking your upgrade path). Otherwise the majority of it is compiled within the DLLs so you'd need source code to make those modifications. Could also use some jQuery to make modifications, might be a plug-in for that already though.
Interesting concept on being able to control the markup better. Using out of the box page layouts, page templates, doc types, and transformations will allow you that same control. Take a look at some of the responses on this LinkedIn conversation regarding development modes. Only reason I bring this up is think about doing an upgrade or what you're currently doing. How much easier would it be for you and the client if you didn't have to charge them an arm and a leg every time they needed a hotfix applied or an upgrade or some simple feature added?