Sorry, are you saying that it's the effort for you to build a native Android app, a native iOS app, a native Windows Phone app, and a mobile web app combined add up to more than the effort it takes to make a single web app and get it to run well on Phonegap on multiple platforms?
That's a pretty bold statement. Are you on a big team? I would expect you'd need at least a half dozen developers to pull off four separate apps, while I can easily imagine a single person building a web app that could run well in PhoneGap.
I just spent six months building a quite complex single page web app with the hope that I could in the future package it in PhoneGap (or similar), so if what you're saying is true then I'm fucked, because it would take me easily a full year to build 3 native apps of the same complexity. Probably much longer.