On device apps/software vs. web apps - which is better for schools?

Apps, software, web apps - they are all tools to use on computing devices to get things done. I use 95% web apps (Gmail, iGoogle, Evernote, Google Calendar, Google Docs, Tweetdeck, Prezi, etc) and occasionally use Microsoft Office for some things I haven't uploaded to Docs yet. Web apps are free, easy to use, accessible anywhere, and platform independent.

Apps and software are sometimes free, usually still easy to use, not accessible anywhere (although your files can be if you use a file sync service) and dependent on your platform. Windows, Mac, iOS, Android, Blacberry, webOS, smartphone vs. tablet, etc.

So, which should schools be using? I think schools should look at web apps whenever possible. There are thousands of blogs and sites that talk about free web apps and what web apps replace what software, etc. For the most part, everything that students need to do can be done with web apps. There is also no updating for IT to worry about, no lost dollars if you switch platforms, and any one can access them no matter what platform they are on. This is really important if you are working towards BYOD (Bring Your Own Device). It would be terrible to have a lesson that relies on a specific app and then a student or teacher has a device that doesn't have that app. With a web app, that is no longer a concern. It's one of the reasons I love Google Chrome OS and Chromebooks.

Don't get me wrong, I have tons of apps on my TouchPad and Android phone. But, whenever I share a service or app with my colleagues or students, I always make sure that there are web apps of it. There may be on device apps for these services too, like Evernote, but they also have a web app. Most of what I use with my students for classes are web apps or web sites that they can access from anywhere.

So, what do you think? On device apps or web apps? And why?

Are there on device apps that you have to have that you can't find a web app version of?