Hmm not good coming from the author of a program to edit a reflowable format.
Let's see if we can address some of your concerns:
1) Multi-col: The whole point of multicolumn layouts is that humans find it hard to read long lines. With a reflowable format you dont have long lines in the first place.
2) Floating sidebars:
Again the whole point of floating sidebars is to use the wide margin spaces available in fixed size layouts for large pages. There's no real functional difference between a floating sidebar and a centered block one. You're just used to seeing floating sidebars so you think asides must always be in the form of floating sidebars. Except perhaps that block ones interrupt reading flow a bit.
3) Code listings
You can put your code listing into a whitespace: pre element in which case it wont wrap and will look just as good as a PDF on small screen (better since you will be able to change the font size).
As for your dislike of reST, that's between you and reST
