"Please don't complain about tangential annoyances—things like article or website formats, name collisions, or back-button breakage. They're too common to be interesting."
The UX of a date picker on the page doesn't clear that bar. That doesn't mean it's unimportant, just that the top of an HN page is not the appropriate context for it. Unless, of course, the story is about the UX of date pickers!
I suppose we could let people mark their own comments off topic, which would drop them to the bottom of the page...