Designers steal ideas? Openly? Umm where do I begin? I mean to some degree it falls in a legal "recipe copyright" zone...That I understand, and as someone who has copyright in multiple countries, I can say that openly admitting to stealing other peoples IP is an unwise move.
So, just to note:
Copyright applies to specific expressions, not to "ideas". Moreover, copyright does not apply to systems, processes, or rules themselves - only to a specific expression of them.
Thus, yes, designers use each other's ideas all the time. This summer, I played a one-shot of Draw Steel!, which has a negotiation mechanic that bears a significant resemblance to a negotiation mechanic in an earlier game - Savage Worlds Adventurers Edition, whose negotiating mechanic bears a striking resemblance to a yet-earlier mechanic from a prior game...
The question for designers is not, "Did you get that idea from someone else?" The question is, "In the process, did you make it your own?"