The license is on the underside of the laptop. At least for my ASUS N53SV.
I agree with you that ASUS and other OEM's don't provide install discs anymore. But then, neither does Apple. Everything is being offloaded to the cloud.
My ASUS is also a stop-gap till my next Apple laptop (my trusty black macbook's screen is cracked and doesn't make sense to repair it). I have OS X running in VMWare on my ASUS.