I think that what Zuckerberg said is quite accurate. In my case, while the full quote certainly expanded a lot more, I didn't need it as I had already assumed some of the additional context.

Having experience with both JS/CSS3/HTML5 and native mobile apps, I think it's hard to make an argument that the "HTML5" route was ever appropriate for a Facebook app. For a browser-based experience, sure, but for an app (where users have an different expectation of functionality and experience), they made the wrong choice from the get-go. Sure it was easier, and they could re-use a lot of existing code & functionality, and it probably cost less too (no need to hire Java and Objective C developers), but it came back around and wound up costing more in the long run.

As devices get faster and faster, and HTML5 mobile frameworks are further optimized (speaking of which, Sencha announced today the pending release of Touch 2.1 with some sizable speed increases), the "HTML5" route may very well become a legitimate contender for large-scale mobile apps. For now, I believe it's best suited for less complex implementations.