They're trying to be nicer to the humans. (Though IMO, any human who wanted to be kind to himself would just not use PHP to begin wtih.)
Right now those humans would not choose to start a project in php, but a few years ago there were not too much alternatives. It's not for nothing that the world's second biggest website is written in php.
Do you mean Facebook? They only use PHP for templating and legacy purposes, as far as I understand. Much of their newer code is written in a variety of languages, including C++, Python and Erlang.
In the immortal words, I am not even able rightly to apprehend the kind of confusion of ideas that could provoke a question like that.
Slower parsing, really? Is that what you are worrying about?
Any site that needs real speed will be using APC or eAccelerator anyway, so that's not really relevant.
It's just an additional alias in the grammar, no real measurable slow down given the size of the parser as is.