And why, as end-user, do i care this? I need something that works. A newer version of xorg was apparently more important to drivers compatibility for the package maintainers. For me as user it was the other way around. And it is not trivially possible with Ubuntu to use an older version of xorg.
To elaborate on that: somewhere along the road the xorg developers decided to break something. How hard is it to design something and keep it (forward) compatible? Apparently for xorg very hard. I totally am ready to believe they had their reasons to do so, but you simply cannot expect all other involved developers to run behind them, within months, if they make make a change breaking stuff, totally ignoring the significant amount of testing the AMD developers would have to do. And surely the AMD developers still get the blame simply because they are 'closed source'.
From an idealistic stance of view, you are totally right. In an ideal world those drivers would be open source. From a practical stance of view, developers all over the world, both open and closed source, are hands tied down on license or agreements. And users just want something that works, not necessarily the latest greatest shiniest.
In case of Ubuntu 16.04 the AMD user is left in the cold, no matter who to blame. And this is why people who say 'Linux will never be ready for the desktop' are proven right. I did, and do, use and love Linux but in all fairness it has been a constant struggle, swimming upstream, because design decisions like those are not made from a user stance of view, and because i do not want to dedicate my life to the OS running on my computer. I just want to use my computer.