1. It wouldn’t be any work for them, since they clearly already have an internal one they use for both FeedDemon and NetNewsWire.
2. Handing the API out is a simple way to have people write programs for your service.
3. Users, like me, may want to use NewGator on their Linux machines, but don’t like the web interface.

I’ve specified an alternate mechanism for quoting things from NetNewsWire and sending them to MarsEdit to post about, to wit:

[#title#](#url#):
> #body#

This works superficially, but if the body I’m quoting has more than one paragraph, clearly only the first one will have the quoting caret in front of it.

Gruber says:

Any decent text editor should make email-style quoting easy …

But I don’t think he imagined the use cases that Markdown might encounter, which is interesting because there’s a quote from him displayed on MarsEdit’s website stating that nearly everything he writes for Daring Fireball is through MarsEdit. Hmmm.