I completely agree that web sites should be accessible to all visitors. The problem seems to be that the developers on many sites have infrastructure that is half a decade old and they are only making minor tweaks. It's easier for them to create a new dev group to build an app than to disturb their delicate website house of cards.

Then there is the issue of privileges available to apps vs. web sites; until the browser supports webkitUploadAddressBook({ stealthy: true }) there will be a strong incentive to develop an app.