I'd have to agree. To add to your points though, I like to think of Ideas and Execution lying in a spectrum between Genius and Obvious.
You can take an obvious idea (a social network to connect friends circa 2004), add genius execution to it in terms of adoption and growth, and win.
You can take a genius idea (crunch every page in the web and spit out search results in seconds), keep the execution in terms of UI and experience really obvious and win.
You can even take an obvious idea, apply an obvious execution strategy to it, and steadily grow (or at least play a strong catch up).
The scary part is when you mix a genius idea with genius execution - and risk getting having brilliant app fly over the head.
IMHO bad things start to happen when we start falling blindly in love with our own intellect.
I disagree with premise 1. Sure there is execution risk, but it is not too hard to sort bad ideas from good one provided you actually have some good ideas. The problem is most of the time you are sorting through bad ideas trying to pick the least worst.
In regards 2 there are very few “buyers" of ideas (if anyone knows of any please let me know). VCs and angels have not shown much interest for ideas until they have been proven. I personally think that given the rarity of truly good ideas this is not optimal. Investors that could bring together the best ideas with the best teams could create real value.
Regarding 2, the idea "buyers" are not VCs and angels, they're the other people you need to implement your idea. The savvy engineers and business people you want for your initial team are probably the kind of people to have great ideas themselves. And if they're already working on them, your idea ain't special.
VC and angels are most defiantly not buyers of ideas, but very few engineers or business people are buyers of ideas either. This is the reason you don’t have to worry about sharing your ideas (in general) since nobody cares about anyone else’s idea even if it is fantastic.
If your idea is no better than everyone else's it is not a truly good idea.
1. History has demonstrated that you can't really tell how a good an idea is until you actually try to execute it. ("Dig here, there might be gold.")
2. The potential "buyers" for these ideas already have plenty of ideas that they would rather work on.