But it turns out that websites are really freaking easy to update, and apps are not. And now you have two completely disparate codebases to maintain. So once something rolls out on the web property, the shiny new app is not so shiny and new, and may be missing critical features. Some companies do this well, Facebook for example finally has an app that more usable than the mobile site IMO. But Facebook has serious resources to dedicate to this type of thing, and it took years for them to get to the point they are at now, their app was barely usable for a long time.
Case in point: I've been using Piazza for a number of classes over the last few years. They have an iOS app, and a lot of people in my classes have expressed that they are glad of this and use it exclusively. But it hasn't been updated for the iPhone 5 so the app display is cropped. Worse yet, there is now a course documents section that some teachers use almost exclusively, that you simply can't get to on the app. And the web page itself does not work terribly well on mobile Safari. So I hardly ever use it on my phone, and my overall impression of Piazza has seriously declined because I've spent so much time cursing the (lack of) usability on my phone. Plus you get the #doorslam every time you try to go to the web site on an iOS device.