Why go with PHP and have to roll your own framework, when you can go with something else, and leverage all the great work that has been done by the Django/Rails/whatever folks? This post tells me all that they have accomplished, which is cool, but doesn't tell the most important thing: why did they choose PHP?
I have to take missions in PHP (Symfony2 and Zend Framework) from time to time, and it really makes me appreciate how much more advanced Rails is. And I don't mean advanced as giving me lots of options for doing obscure things. I mean advanced as doing for me all the repetitive stuff that I would have to do anyway, so that I have much less code to write, much less room to introduce bugs, and I can focus on what really matters. The PHP ecosystem is trying to replicate that, but so far, it's still quite far behind.