The real problem is that it's REALLY hard to tell which is the better idea when things are just at an idea stage.

I bet that when they were first proposed (before building anything or seeing adoption numbers) WebTV seemed like a MUCH better idea than Twitter. (not that they're comparable services just that if I told you that I wanted to let people use the internet from their living room, that would sound more exciting and useful than creating a service where people write 140 character blog posts).

Quality of idea just might not be a valuable metric.