HN Guidelines[1] state that original article titles should be used as the title on HN (though I agree that it's sometimes to the detriment of HN readers).
Indeed, title changes (by either submitter or an admin) which improve the original title, without adding spin or sizzle, should be welcomed.
The mechanistic insistence on original titles often gets things wrong, leaving a title in place that "buries the lede" (the actually new nugget in a particular story) or includes its own misleading spin. People then either miss or waste time on stories, when a few reasonable extra words in the title would have helped.
Possible experiments to address this might include:
• Adding a separately-voted 'title tournament' for each story, in which the original title, submission title, and others audience-submitted compete. (They're not competing for which gets the story the most upvotes, but which best describes the item.)
• Allowing a subhead per story, where either the original subhead or some other pull-up excerpt can appear for context. (This could be from the OP, admins, a group tournament, or even just wiki-style.)
[1] http://ycombinator.com/newsguidelines.html