Brion,
That's all fine. And in the world we would like to live in, people would write compliant clients, and always use a strict HTML parser, and nothing would ever break.
That isn't the real world.
The world you have, that you have to deal with, is that in the absence of the present API until a year ago, and the edit API a month ago, people did whatever they could make work. And there is a huge amount out there. It may be frustrating as all hell, but it is reality.
For myself, I started with a copy of the python stuff about two years ago, fixing all sorts of cruft along the way. If something broke, I went and looked at the current copy (svn update on a different copy, not what I use). I've replaced various bits with API calls, particularly because doing a edit op when all you want is to *read* the page wikitext is silly.
In this case I looked at it, found the missing wpSection parameter easily, and fixed that. Then couldn't find the other. (Misza hadn't checked it in yet ;-). So I'm not complaining about the stuff I'm doing, but I am concerned about the 99.9% of the users that don't know how to just go fix it. A number of them are on the en.wikt and will turn to me for help ...
I'm sorry to say that it is simply a requirement that the GUI be treated as a stabilized API that cannot be changed without checking the effect on client software, and that this state of affairs will continue until the pybot et al are completely converted to the API, and time enough has passed that people have gotten the API version and are using it. This probably means a year or more.
I know you *really* don't like it. I wouldn't either. But the way it is, it is.
with my best regards, Robert