Gotta say that I don't get it either. They've basically just added yet-another-HTML-templating system into the mix. Question not answered: "For the love of all that is holy, why?"
PHP is an HTML templating system. Tacking on yet another one strikes me as more than a little pointless.
By that reasoning, we should just code a whole site in a single PHP page that handles both the backend processing and the display layer and generation of HTML.
It's not about decreasing the number of files (to look into to find bugs), it's about organizing the code into logical pieces that are more manageable.
PHP is an HTML templating system. Tacking on yet another one strikes me as more than a little pointless.