Converting a mobile webapp to BB10 to native app takes merely few hours. BB10 supports Phonegap out of the box (their dev tools have simulator for it). They have their own version of something very similar to Phonegap but a little richer. You can port any Phonegap app to BB10 and use their JS API's for deeper integration.
BB10 is RIM betting on HTML5 for native apps as well. If they can optimize the experience nearly as good as native Java apps - this could be the next tide. You gotta look at the future where developing for 5-6 platforms would be a pain. Microsoft is betting on similar approach for Windows 8.
Win is at the next tide - not the one that Apple rode 5 years ago.
Native apps are much nicer and easier to code, regardless of the platform. And don't even get me started on the mess that is trying to use JS frameworks such as Jquery mobile to actually do something useful. Such as facebook or twitter integration.
Cross platform app development is a good ideal but none of the current platforms can do it in a way that isn't a horrendous pain.
Blackberry doesn't have a choice. They're in a tough spot. They need to "skip" a generation, if they have any hope of survival.
Things are moving toward web/html5 tech and that is the future. Not now, but in a few years. All of the direct-hardware-access stuff is being worked on right now.
Even now, you can build metro/Windows 8 apps using html5. There's Firefox OS. WebOS is barely alive, but still kicking.
And, of course, there's the simple argument that the most important and popular app on both iOS and Android is the web browser.
The reason the iPhone is so popular is because 1) people are excited about it 2) great native apps make people excited because they do useful or fun things quickly 3) the iPhone is part of a rich ecosystem with services for music and apps. The iPhone ecosystem includes cloud and desktop integration along with support from the top rated e-commerce site as well as local support with award winner retail stores. That great customer service matters a lot to mobile phone customers who often expect a lot from their phones. With BlackBerry you get a phone from a carrier which has a poorly trained sales staff which cannot help you and often does not care. If I have an issue with my iPhone I can go into a nearby Apple Store and have my issues resolved quickly, and if necessary, they give me replacement hardware. And BlackBerry is putting out a better web browser? Better than what? Better than the poor browser they had previously I suppose. Apple has had a great browser from the beginning. BlackBerry does not get it. And if they want to catch up they need to do more than tweak their system. There should be an entire ecosystem built around it, but it is already too late. Android is already eating up all the space which Apple has not and Windows Phone is scrounging for scraps. Very little will be left for BlackBerry. They never innovated after they reached their peak. That's how the mighty fall. I hope Apple keeps innovating. I think they are due to push it this coming year. More integration between the iPhone with other aspects of our lives from TV to our cars would be great and we've already seen rumors that is coming.