Nellisir said:
2 points, I think. 1- You're not doing an entirely new layout. You're revising an existing one. You don't have to recreate any style aspects; they just need to be resituated in the document. 2 - Compared to the amount of time you spent writing and creating the manuscript, is doing a second layout really a significant time drain?
It could very well being a time drain if you're not doing layouts that often (as in: "I've written 7 books, so I've done 7 layouts").
Most people are publishing eBooks, because they love writing new material. Maybe that's the main reason layout, editing and art fall somewhat short sometimes. (IMHO by far the most important aspect of every RPG book, electronic or otherwise, is the content.)
Most people will loose money by making (only) PDFs. The amount of time involved, and the start-up costs are tremendous. So what some people might do is cutting these costs (less time spend on layout, few if any professional software) wherever possible. And who could blame them?
You can't stop the "hobby publishers", and IMHO you shouldn't even try. The only way to establish a standard would be if the customers would honor the effort - if I'd spend an additional X hours doing the layout, the product will likely sell Y times better (similar to: if I'd spend $X more on illustrations, ...)
I will do two layouts for every published layout (Complete Spell Cards being an exception for obvious reasons), but that's because I actually like doing the layout, and I'm pretty fast at it. On the other hand I'm not a big fan of prestige class design, so obviously you'll see less of those in my books. Sure, there'll be some people who'll complain ("Me want PrCs!"), but my answer to these people would be: well, then get a book with lots of prestige classes.
Same goes for layout. If you're looking for a PDF with both on-screen and printer-friendly layout, then by all means buy those.
If these "dual-layout" PDFs should someday sell siginifcantly better than others, I'd say most publishers will do this. Otherwise they won't.
One thing won't happen: "dual-layouts" bringing fresh customers to RPG Now. That's something for "expert customers" only.
To make that clear: I'd say "dual-layout" is a good thing. It's all about making PDFs different (and in a way even superior) to printed books. But you can't demand it (it's like saying: "Great product, Ye Small Publisher, but I won't buy it unless at least half of your illustrations are by Todd Lockwood.")
Note: I've got the flu, so don't judge me too harsh

Hope I made a point anyway...
[Edit: removed the most blatant errors...]