True, of course.

Assuming a startup falls in the latter category, coming up with a good monetization for a B2C web-app is challenging.

Majority of the apps I use daily fall into the 'nice to have' category. Most dont provide me the value to the point that I'm willing to pay for them.

And seeking out that distinction - between the 'nice to have' and 'must have' categories is what turns several of my ideas into vaporware

Can you give a bit of insight into this? It seems to me that facebook or twitter are simply a reinvention of the same kinds of companies that started and failed in the dotcom era.

I thought the lesson learned was that technology companies are not magic. And one should invest in companies with a sound business model. What about twitter or facebook invalidates this?

The lesson learned was to not to avoid companies that aren't currently profitable. It was to avoid companies that could never be profitable-- e.g. because they were buying users. Facebook and Twitter aren't doing that.