Sure, those people would also be able to learn Python, Ruby, or whatever the flavor of the month is. But it would take you significantly longer to train them to work on your project. And they might want more money if they realize they now have a more valuable skill ;).
I believe this is why Facebook still uses PHP.
In that light: a new PHP framework that makes things even easier is a good thing.
That said, it's NOT true that Facebook still uses PHP because they get cheap developer power. See this Quora thread: http://www.quora.com/Why-hasn-t-Facebook-migrated-away-from-...
From FB's former Director of Engineering:
The reason Facebook hasn't migrated away from PHP is because it has incumbent inertia (it's what's there) and Facebook's engineers have managed to work around many of its flaws [...]
"Tons of problems and weaknesses" is largely untrue at this point. Many of the problems that were traditionally pointed to were corrected in 5 and 5.3. There is no interest in breaking backwards compatibility, so the built-in function parameter order inconsistencies are still valid. Most frameworks work around this issue with an OOP wrapper for array and string operations.
It is difficult to find good dev-power for PHP that's cheap. I've tried. You can find many people who have a basic level of PHP knowledge and refer to web apps as "scripts". Finding people who have an understanding of OOP and modern development techniques is much harder and more expensive.
Here's why I program web apps in PHP: it works and I know it well. If I need a library for something web related, I can assume it will be available as open-source. I don't have concerns that I can make a PHP application scale if I need to. When features don't make sense to implement in PHP, I'll snap them off and implement them in the most appropriate language in the background. Most of the heavy-lifting for web applications typically happens in the background.
Definitely hear you on the lack of PHP developers with an understanding of OOP and all though. Seen it myself when my previous company tried to hire one, the 'range' of people applying is incredible.
If it really bugs you it could easily be solved with a few helper/wrapper functions.
(Besides that, regarding elegance of syntax, there's no doubt that most other languages used for web dev'ing are lightyears ahead of PHP.)