The only one way I can argue for the need of more than quad cores is to allow for a future unknown resource-intensive application. But for most present day applications, even for Graphics rendering (which by the way - has its own dedicated processor!), spending money on more cores is purely money down the drain. Parallelization of algorithms is actually not a trivial task at all.
Let's take Visual Studio as an example. It can compile each project in a separate thread. In a large solution, each additional core will cut the total compiling time in half. If it takes an hour to compile on a single core, a dual 8-core xeon will take about 4 minutes (or 2 if hyper threading is really that good). I'd call that money well spent.
And the parallelization here is actually quite simple as it is done on the project level. No complicated algorithms are needed.