One should be able to compile a web app into a downloadable package, with capabilities to run the app completely offline. Until that web will always be second best to fully native. Performance is getting close enough though.
"The ultimate purpose of PhoneGap is to cease to exist."
http://phonegap.com/2012/05/09/phonegap-beliefs-goals-and-ph...
The issue is that HTML5 apps don't install and run the same way (not as convenient).