Because ideas are not easily "excludable" ( http://en.wikipedia.org/wiki/Excludability ). How can you sell it if you're giving it away for free on the site? How can you buy it if you can't read about it?
That doesn't mean that an idea has no value, it means that it's impossible to transform into money. Or, if not quite impossible, that the transaction costs outweigh the value of such a market (I'm not convinced of the value of the original poster's idea:-)
BTW, I explained this a year ago:
http://journal.dedasys.com/articles/2007/04/26/ideas-are-wor...
There are numerous well paid professions where people are paid solely to come up with ideas. Like the poster said, the reputation of the idea creator is considered by the buyer/employer before the ideas are payed for.
So that quote is a little off.
--Ok. If you say ideas have a real value, then why there is not market for it? Why there is no website where you can sell your great ideas to the highest bidder?
sorry, but ideas are just that. worth 0. It takes hard work and execution to make an idea worth something. Therefore, the execution is the value making part of it. Without it, the idea will just be a day dream.