Whilst mostly true, to truly maintain wealth over many generations, you have to be very consistent with the culture that you pass down.

If Gabe is smart (I assume he is), he will know about the third generation problem, and how to mitigate it. He will talk about it with his kids and grandkids when they are old enough to understand. Building a culture around a shared set of values, making then understand that their success is built on providing the best experience to gamers that they can.

The other key thing, is to make the next generations understand that, whilst 10 years may seek like a long time, it really isn't.