See, I constantly hear this argument - why do we need standalone apps when the best mobile browser is on the device and you can use any application from the browser itself ?

This doesn't cut with me personally. Not on a mobile device. And forget the fact that Nokia calls its a mobile computer - that doesn't in any way equate with how I use a actual desktop computer. You DO NOT want to copy how a user uses a desktop computer method and paradigm to a mobile device - irrespective of what you call the mobile device. Simply because it is a MOBILE device. You cant copy over the desktop paradigm to a mobile device.

And if the rationale that we can use browser based apps on the N900 (or any mobile device) worked fine, then pray tell me, why did Nokia go and integrate Social apps into the platform itself ? They could have just told use, use those IM / social services from the browser.

That's because standalone apps offer the one big advantage over browser based apps - Integration.

This meme of "go use a browser based app" is because we (some of us) are making excuses for not having good quality standalone apps for N900 and rationalize it by saying you can do everything from the browser. Any good UI design guy will tell you a mobile device has to be geared to mobile usage - which a full fledged desktop browser is not.

I don't understand this terminology distinction - N900 is not a smartphone. OK, I will agree with the terminology, but irrespective it is a mobile device - the same kind a smartphone is. Same size, same pocketability, same form factor. So how can the usage cases be THAT different from a smartphone. I can understand the extras the the N900 provides - more power, more opennesss etc, but that doesn't mean the smartphone use cases vanish .