Earlier quoted context omitted.
This is pretty much spot on. I believe that the lack of "strong-D" Design you refer to is because Linux's desktop is pretty much the ultimate committee-driven project. It's very democratic: great for preventing abuse, but rather bad when it comes to vision. Most of us here know how difficult it is for one person in a company to drive an idea through without it being diluted; countless product companies have gone bust…
Maybe collaborative development is incapable of producing something as complex and difficult as a clean, well-designed desktop environment and API? Forking, competing spinoffs, factionalism are all useful things in some ways, but they're death to this kind of project. The Rails community seems to manage.
Collaborative development does rather well with developer tools.