And community. I am using both PHP and Python because of two widely different communities and approaches to solve problems. For example, Python is the language with the largest and most robust collection of scientific software bindings. Python users tend to take a bit more time to implement things, but they do it in a very robust way. Java is pushing a bit, but Python stays the king.

On the other hand, for everything a little bit "web" related, you can find a stack load of easy to use PHP code. They are also usually "pure" PHP, making them easy to integrate in your own framework/system. Usually the PHP community at large is very fast at getting things done in a simple way (sometimes a bit ugly, but this is improving drastically).

Note: This is of course a bit of a caricature what I wrote, but in essence, you cannot ignore the community/ecosystem supporting your language.