[lorenzhs]

It's pretty clear that he's not talking about asymptotically faster than n log(n), but faster on real machines. While optimisations---like in-place partitioning, tail recursion, and using insertion sort when your problem size falls below a threshold (e.g. less than 16 objects)---won't change asymptotical complexity, they will make your implementation run five times faster.

Asymptotic notation hides the constant factors, which is good when you're talking about asymptotic growth. But when you want a practically fast algorithm, constant factors matter!