[markokocic]

Because it might be the best option for a next few years? I'm not saying it is, but some people did a right choice "locking" themselves to Adobe-only infrastructure (Flash), Apple-only infrastructure (iOS/Objective-C), Microsoft-only infrastructure (Windows/Office/.NET), ...

[nir]

When you're on the client side you don't have much of a choice. On the server, there are various options.

And even then, GAE is more risky than, say, .Net - since you never actually buy the platform, you're subject to Google's changing prices and product priorities.