I think PHP scales well because Apache scales well because the Web scales well. PHP doesn’t try to reinvent the wheel; it simply tries to fit into the existing paradigm, and this is the beauty of it.
Read on shiflett.org after a small pointer by Slashdot into the right direction. This guy really knows what he is writing – or at least it seems to me as I think exactly the same way as he does (which is a somewhat arrogant way of saying things, I suppose :-)).
gnegg 