10.6.8 is Lion - 10.8.4 is Mountain Lion. He probably decided, like me, that it wasn't worth the cost of upgrading because almost all the improvements are to do with compatibility with mobile devices -
Oh how wrong you can be.
I'll grant you 10.6 was a decent OS.
I'll grant you 10.7 wasn't much of an upgrade to write home about.
However 10.6 -> 10.8 has seen improvements in many areas, "compatibility with mobile devices" is just a tiny portion.