Does it matter? I think the point is that (Great People) + (Profitable Idea) = (Success)
Consider: The variant of (Poor People) + (Profitable Idea) = (50/50 Success) and the variant of (Great People) + (Unprofitable Idea) = (Failure). If (Great People) it is far easier to get (Profitable Idea) then to change (Poor People) to (Great People).
To use your example, if you're making a Ruby IDE and no one pays you, you will never be profitable. If you make a Greate Ruby IDE and no one pays you, you will never be profitable. Discovering that MMORPG's are more profitable one day, you build one, and people pay you, you might be profitable. You could consider the time you spent on your Ruby IDE a waste, or you could consider that you've learned something about software development as a business. It is far easier to change the idea then the people.
But that's implying that working at Google won't be as rewarding. There's a lot of pressure to execute and iterate and so on when you're doing a startup. People sometimes forget to sit down and relax. Being in a less risky, less stressful position at Google can give you the important insights you need when you really start your business.
I also submit that it'll be easier to quit Google when you've discovered your home run idea than to change your entire business.
"Being in a less risky, less stressful position at Google can give you the important insights you need when you really start your business."
You could not be more wrong on this point. Being at google is a recipe for complacency. Quitting your job is incentive to actually figure out how to build something good. Because it's do that or fail.
For example if someone starts a dating site but later transforms into a general social network, I would call that a complete transformation.
However if you start out making a ruby IDE but later realizes that real money is in MMORPGs or whatever, well you might have as well as waited.