Well, I'm sorry, but in my book if you make something Open Source, stay as the maintainer for a long time yet fix no bugs or make no improvements, don't register the trademark AND publicly complain when people try to improve the situation, you're like a parent who doesn't treat his child well. And in most societies I know of, that's a valid reason to lose your rights as a parent.
Harsh comparison, but I feel it reflect the current situation well.
That's a sillily emotionally-loaded comparison. An open source project is hardly a child, neglected or otherwise.
The proper course of action here is a fork, which has no equivalent in your analogy. Gruber's Markdown remains as he likes it, under the name it's already widely known as. The new Markdown-based language picks a suitably disambiguated name and becomes what its maintainers want it to be.
Not all forks pick "suitably disambiguated" names. In fact most hostile forks actually picked a name that was making fun of the original. Or just piggy backed the "brand". The only cases where this didn't happen was where trademarks were involved (OpenOffice.org, Hudson), and even those cases might imply pointing fingers (open has far more restrictive connotations in the software world than libre).
And in this case I do hope that the hostile fork actually becomes what it aims for: standard/common and basically makes everyone forget about Markdown.pl.
Harsh comparison, but I feel it reflect the current situation well.