I don't see why every distribution out there should invest its resources into the same areas.
- Redhat seems to invest a lot of effort into "Linux Plumbing" and as a non-Redhat user I'm very grateful for it.
- Ubuntu seems to invest a lot of effort into integrating, launchpad, translations, "community", evangelising (like with their "shipit" - cds sent for free), etc - and as a non-Ubuntu user I'm also grateful for all that.
There's clearly a market of users out there that only started considering Linux when Ubuntu appeared. Increasing userbase is very important. New Linux developers are a subset of the total Linux users after all; mindshare matters.
Linux Plumbing is important but not the only thing that needs work, just take the MacOS X example for instance.
Apple's iPhone is another example of a different focus - the hardware is more or less the same as all those Palm, WinCE, Pocket PC, Symbian devices. The plumbing didn't really make a difference. But the UI, integration, infrastructure (appstore) mattered a lot. Now everybody else learned their lesson, and we'll all get phones with better user interfaces (modulo some bad rip-offs too). What Apple did could in theory have been done by us Linux people or other proprietary companies years ago - but they went out and JFDI.
Ubuntu has a similar role IMHO - it tries to focus on something else; it could be an evolutionary dead-end, or it could pay off, in which case the other distros will also have learned something in the process. All good.