It all depends on the idea: some are just so much better than others...
Larry and Sergey's PageRank isn't a new application level idea (as search engines already existed) but rather a better implementation of an existing application level idea.
Perhaps you could say that twitter is an accidental success that is much more interesting than the original vision.
"@Jack was still just an engineer, and the service was only a few months old when the group acquired Twitter.com and re-branded. Back then, we had no character limit on our system. Messages longer than 160 characters (the common SMS carrier limit) were split into multiple texts and delivered (somewhat) sequentially. There were other bugs, and a mounting SMS bill. The team decided to place a limit on the number of characters that would go out via SMS for each post. They settled on 140, in order to leave room for the username and the colon in front of the message."
http://www.140characters.com/2009/01/30/how-twitter-was-born...
1) idea: A mental model of the way something works, has worked, or could work in the future. (e.g. page rank)
2) idea: A plan. (e.g. Twitter sponsoring SxSw)
(I realize the two senses of the word are related, but for our purposes they are functionally distinct.)
Anyway, good ideas of both types can create value, but they do so in completely different ways and require completely different resources, strategies, and tactics to execute.
In any case the entire concept of starting a business around an idea is stupid to begin with. Twitter and Google aren't the result of a good idea, they're the result of thousands of good ideas, a sufficient quantity of which were executed well enough to keep the lights on. Real business people don't start with a business idea, they start with an asset they want to capture, and then come up with several dozen ideas for capturing that asset and then pick the best ones to push through the dip.
Perhaps a stupid question: what do you mean by asset in this case?
An asset is a resource that you create which you can later harvest for money. For example, let's say you are an event promoter. In this case your asset is your mailing list, because having a list of 300k people willing to read about your events allows you to go to night clubs and ask for $20k in exchange for sending out a blast to your followers.
So once you decide that the asset you are creating is the list of people willing to hear about your events, there are any number of ways you can go about creating this list. You can sign people up who go to events, run contests, find local people on twitter and start conversations with them, create a website and run google ads to get people to it, etc.
The point is that smart entrepreneurs don't start with ideas, because ideas usually fail and once they fail you're fucked. Rather, they come up with an asset they know is valuable, and then come up with 50 ways to build that asset, knowing that some of them will fail. This way even if some of your ideas are only hit 10% of your target goal for growing the asset, at least you spent that time growing an asset that you can monetize in the future and you don't have to start all over.
Business ideas are for chumps.