Exactly. For what I consider to be the best idea I ever had, I was able to attract three very talented people to apply to Y Combinator with me, with a 25/25/25/25 split. The value of my idea was that it made people excited in its potential and my 25% was only valuable with the contributions of my partners.
If I were in a startup, I'd want it to be a total free-for-all where new ideas are valued. Not one where the older ideas are considered to be worth more. That's totally backwards -- your ideas about the business are likely to change and become more valuable as you gain experience and talk with customers. And unless you prefer co-founders who treat it as a 9 to 5 job where they are mere implementors, they will be coming up with many of the important ideas too.
The worth of the initial idea is measured in the fact that you got other people to even commit to the project. Call that a victory and move on.