The vast majority of applications you COULD write would work just fine as web applications. If you want to reach the largest audience with the least API-lock-in, think HTML/Javascript. Frameworks like Sancha, Worklight, Sproutcore, Phonegap, Rhodes, and jQueryMobile are providing an extremely good API that allows you to target the web browser so that you not only can have users on iOS and Android, but also Blackberry, Symbian, Windows Mobile, webOS, and any other touch-based web browser.
These frameworks allow you to take advantage of the new features of HTML5 such as local/offline SQLight storage, canvas, drag/drop, OpenGL, etc. The main downsides are that you DON'T get listed in the various markets, you don't have access to many platform-specific features - notifications are still a little tricky, but I'm sure that there will be an open source app to handle web-based notifications in a multi-platform way in the future.
I wish most of the apps in the Android/iOS Markets would just go away and become web sites, because they have no purpose as downloaded apps, including many games.