I think your point about rapid distribution and iteration is the most compelling reason.

Anecdotally, I've heard from a number of engineers and technical leads working on mobile-first startups that they started out by building HTML5 mobile apps and driving traffic to it (vs. native first) to better understand what users want before starting native application development from a test-learn-iterate standpoint.

Being able to make rapid changes based on user behavior and feedback significantly de-risks the chance of "missing the target" at the outset.