So the only advantage is that when the OS upgrades\changes the app will need to be tested? Surly when the OS changes there will be a new browser? Doesn't that require the same testing?
If this is that much of a worry you can write your application in a language like Java, which will provide you with your platform independence, and eliminate most of the downsides vs a web browser. (Apart from the performance.)
And before you start slagging people off stop to think for a second, you actually dont know who I am, nor where I work. I can assure you that you are incorrect in your assumption.
The whole point of web services is because they are being delivered to the general public and you have no idea what platform they will land on, so the browser is restricted on what it can do. The enterprise does not have these sorts of problems. (Generally anyway, if they do then the web is the way forward.)
As for deployment, you know you dont need to have a bod walking around with a floppy any more, right? This is a good use for the web, have a deployment page, one click and its installing. Upgrading? That's not hard, look at any app out there for an example of self updating. (And its trivial to implement, if you really wanted to it can be done in a batch file, though I'd rather have it in code.)
Ill admit for large companies with lots of small offices all over the place which do not have a fast network infrastructure browser based apps would be the way forward, so maybe thats where you work, however all the experience I have is in the financial industry where there is no bandwidth issues to worry about.