Why does Mathematica crash at a certain recursion depth?

If I enter

Block[{$  RecursionLimit = 70000}, x = x + 1] 

I get

$  RecursionLimit: Recursion depth of 70000 exceeded during evaluation of 1+x. 

But at $ RecursionLimit = 80000, Mathematica crashes (i.e. goes unresponsive for a little while and then clears all variables). Why is this? Is there some limiting factor that I can increase to go even further?