No you are correct neither did I see Steve Blank saying there is one. For the 10kh rule to achieve sthg outstanding (write a masterpiece, be a prodigious musician etc.) it seems like it is pretty accurate. For business as always there is no rules ;) but to keep in mind that if you work 50h per week for 5months doing customer development, I would not be surprised that we are not far off. See the example of AirBnB: they said 1000 days in their StartupSchool talk that's way more and they seem pretty bright to me.
Edit the link to Airbnb 1000 days Customer development odyssey ;) http://www.justin.tv/startupschool/b/272180383