Yes, of course. If something is really interesting to the ADHDer, he or she can completely forget every thing else and enter in hyperfocus mode [1].
When one is diagnosed, and aware of this hyperfocus thing, one can use it very efficiently. I, for one, use it to work, with the help of an app called Focus@will, where I can set a timer, and play very loud music, so my brain is focused on the task at hand.
The price is fixed by the editor, there is no state mandated price.
The purpose of the law is to have the same price for a book in every bookshop (with a 5% discount possible). This was supposed to help small booksellers, who could not compete against big corporations. And it kinda worked, as there are more than 3500 independent bookshops in the country.
The split up is not linked to the uniform price, I think it's more a cultural thing.