I worked on the Windows Core UX team. If you think this is an engineering led decision, you have had a different experience with large software organizations than I have.
Even with the Windows 8 UX changes, our most senior engineers were up in arms in open protest and they STILL went through with it.
I've never worked at Microsoft, but have worked at other large software companies. This is 100% a design decision. Engineers like buttons, shortcuts, neat tricks, test tools, secret options, lots of menus, etc.
I also think this is a fairly sensible design decision.
I personally would expect dragging a file to the dock would put the file on the dock, rather than trying to open the file in whatever app you dragged it onto.
Initial designs, sure. When it comes to making trade-offs in features and functionality vs ship dates then that falls into the realm of a Product Manager.
For one, I doubt very much anyone told the developers of the new task bar that it shouldn't be movable to other screen edges. I'm confident that was a design decision by software engineers who deemed it too difficult or time consuming with no regard to how it would impact people who have used that feature since Windows 95.
But even if they had, I don't anyone gets a pass on building a crap product just because they happened to get paid to do so. If your situation is such that you can't risk your job by refusing to do it, you can at least own it and feel an appropriate amount of shame.
I no longer work on Windows or at Microsoft. I expect most engineers don't care enough about Windows to lose their livelihood over it. However many of us did leave the organization after that release.
Even with the Windows 8 UX changes, our most senior engineers were up in arms in open protest and they STILL went through with it.
This is a Product led decision.