I'll stop being mischievousness, but basically the single page app replaces the desktop app of the past, this means:
- We build for the browser not the OS, no dependency in an organisation on windows, linux etc, it will even work on your ipad and mobile. This simplifies desktop support.
- server can easily publish updates frequently, very agile and responsive to change
- Takes advantage of the cloud and collaboration, your web app now has an API (your desktop app didn't!) so you can share data, link to other services and other web apps. Think of google docs, why would you create a word document and email it around or save on a share when you can share it in a web app and even have multiple people edit the document at the same time!
I believe the browser is replacing the OS, not surprisingly it doesn't do a very good job and it's a pain to work with but the end result is so much better for your users.
lastly I don't understand that suggestion ajax was a fad from mid 2000's ?? it's used everywhere and to mostly :) good effect !
it's quite nifty