I think it adds the clarity that they don't think HTML5 is actually bad, but rather that it's still not ready for prime time (for them!)
The many other quotes I've read around the web don't mention this, giving more of a "HTML5 sucks" hint to the quote.
Even when HTML5 will be ready for prime time it could never compare to a native app. This isn't a new issue, cross-platform solutions have been around for ages and they always fell short.
Fell short in what way? Yahoo Mail came out in 1997 and people flocked to use it. You can guess what the UI was like for Yahoo Mail in 1997. But UX isn't only about UI. Being able to shop for a new computer or phone and knowing the stuff I use will continue to work is great UX as well. There are always tradeoffs. I'm tired of the anti-web brigade acting like web development is only good for the developer.
Once upon a time I worked at a company where we developed in a platform called Clipper. We used a cross-compiler to port apps from a PC to an HP-UX system. Although Clipper was based on C and the cross-compiler created C code it was never as optimized as it could be if written from scratch-actually it wasn't even close. In the years since I've heard numerous stories of similar situations. The one size fits all, which was best materialized by Java, never lived up to its name.
You say HTML5 could deliver a unified UX. I disagree. If the problem is the need for unified visual environments then HTML5 is the wrong answer to this problem - CSS is more close to the answer. HTML5 was supposed to be that kick-ass solution for delivering a more robust development platform for the web that could reduce the need for third-party plugins like Flash or Silverlight.
I won't argue that what HTML5 has achieved is no small step. But I wouldn't have high hopes of it ever manage to compare head-to-head with a native app, no matter how mature it would become-and that last part takes a lot of argument since evolution of HTML takes ages.
> You say HTML5 could deliver a unified UX. I disagree.
Me too, I never said that. I said that, using Yahoo Mail as an example, users are willing to sacrifice some integrational purity when ease-of-use and portability are so compelling. Today that balance hasn't been tipped on mobile. I'm willing to bet it will be, eventually.
Sure, if you're comparing like-for-like experience and performance. But HTML5 provides advantages with rapid development, cross platform, distribution etc. over native apps. The debate is whether these advantages are enough to sacrifice the quality of experience and performance provided by a native app (or rather, whether the gap is sufficiently small enough to justify going for HTML5). Zuckerburg's opinion appears to be... yes, but not quite yet.
