Looks like some people have misunderstandings how HTML5 works in this thread so I'll try and clear up some of them.
The only major downside is that using a web-based app as opposed to an actual app on your phone limits the app to phone and OS specific features. Mainly integration with other apps (website can't launch my apps). Features like Bluetooth, GPS, and camera may be hard to work with on a web-based only app
Depends. Lots of "HTML5 development" today is really "WebKit with HTML5" development, so the apps don't work in IE10.
I'm referring to
native HTML 5 apps that you would download and install from the WP8 App Market along with iPhone, Android, and BB app stores. A few of you think I'm referring to web-based apps that you use with your browser. HTML 5 can write native real downloadable apps, which solves your above concerns. They are write once, run anywhere.
Considering how crap PhoneGap's support for Windows Phone 8 is - I wouldn't count on it!
Nope, you must be referring to some specific app in particular called "PhoneGap" I guess? This has nothing to do with that
It depends on the app. HTML will always lag behind the hardware and OS capabilities. The most obvious example I can think of is how would a HTML5 FB app pop toast? People want tighter integration between apps and core OS features and that can really only happen with native apps.
A while back, Mark Zuckerburg wrote a scathing report on HTML5, blaming it on the mobile Facebook app's bad performance, and he had the entire FB app rewritten a few months ago without it. A company called Sencha called him out on this, and said the fault lies not with HTML5 but with Facebook's developers and they set out to prove it. They designed a web-based Facebook completely in HTML 5 called "Fastbook" and it outperforms Facebook's own native mobile app, and includes the same features.
In this case the app IS web based and not native, they designed the web based app just as a concept to show how it can be done correctly. Fastbook can also be written as a native HTML 5 app.
You can read the story here. Unfortunately, because Zuckerberg's incorrect and negative statements made it into mainstream media, people now mistakenly take what he said as gospel, and just repeat what they read on the internet rather than knowing the facts (no offence to the last poster of course)