While "Browser as OS" is what appears to be happening. The browser is the front-end for many applications. Even in the Ajax case, however, the browser is only one piece of the application, and the browser isn't relevant on the server side.
The important point that is missed in the browser wars is that the browser is only the top-most layer in a technology stack that is getting taller.
Look at the latest fad: virtualization. Here's the layers in our "platform".
- Application
- Browser
- "OS"
- Virtualization Engine
- BIOS, ROM's and ASIC's
- Hardware
If we have OS's sitting on the virtualization engine, we make the OS more flexible and portable. Similarly, if we have platform-neutral browser, we make the browser portable. Further, if we have a browser-neutral application, our application is more portable.
While Rapoza's point it good, it conflates the entire technology stack into a single term, "OS", which isn't a very helpful thing to do. It misses the point that "the OS" isn't monolithic, and changes to this technology stack are occurring in many places.
If, however, we write an application that depends on a browser, and that browser is portable enough to meet our objectives, we're happy. If that browser isn't portable enough, then we're forced into multi-browser compatibility, and all the ugly hacks entailed by that. However, in either case, we're divorced from the rest of the technology stack. That's the most important part of this: browsers give us a portable presentation layer.
Note that the thing we call "Linux" is really GNU/Linux, and can be decomposed into the Linux kernel, and the rest of the GNU drivers, file system, commands and utilities. Even the middle bit of our technology stack has layers.
The browser is certainly not the new OS. It's the long-sought-after standard presentation tier of an OS. For years, we've wanted a standard presentation interface, and it's finally arrived. The previous "standard" presentation interfaces have included Curses, CICS, various Forms API's. Even the X-Window system promised a "standard" presentation layer.
All of the previous presentation tiers struck the compromise between hardware-feature-specific and portable by bowing to the vendor's hardware features. Each character-mode terminal or X server had vendor-specific features and extensions. Now, however, the browser swings the compromise the other way, providing a minimal interface that all hardware can support successfully.
The browser isn't the new OS. The browser is the new, standard presentation layer.