If I develop a web app in phonegap, can the same web app be made to run in regular desktops/laptops inside a browser?
Right now you could use browser platform together with Cordova.
You could install it using regular Cordova CLI command
cordova platform add browser
Then installing standard Cordova plugins they provide same programming interface as on the device. Forexample take a look at https://github.com/apache/cordova-plugin-camera/#supported-platforms. Howether support not 100% compatible with device, but Cordova team try bring as much as possible compatible solution to browser as a platform