The only thing web app can make you achieve faster is to reach end user. Anything else will be so much faster using native SDK it is not even funny (assuming you have equal knowledge of either technology).

Sure, but isn't that the key of Lean Startup, which is what OP was hammering on anyway?

Web apps do perform less optimally, but they are also platform independent and can be done quickly. Why not start there, make sure you are hitting the right user needs, then invest in app development?

Because they suck ass.