You make some good points and you are correct that my redesign of the manual is far from ideal in terms of accessibility. I will definitely take these things into consideration and improve upon them. This is not an area I'm familiar with, which is the perfect excuse to go a learn about it!
In regards to the 'experimentation' done by websites. I would say that this 'experimentation' is something that should happen. How else are we supposed to discover new and better ways of doing things than by trying something different. Not all new things are better, and most of them fail. This trial and error, however eventually leads to better design and better 'standard' ways of doing things.
It is unfortunate that today accessibility has fallen down the priority list. Likely, a side effect of all the new ways we can interact with our electronics. So above all let me say thank you! We need people like you who remind developers to keep accessibility a top priority.