First, the cultural.
PHP's community is largely focused on web applications, and has lots of folks that do not have a background outside of PHP or web applications. The PHP culture is generally one of "I'm not interested in understanding why its broken, just give me the code to fix it." If you browse the PHP documentation, you'll notice the comments are riddled with errors, bad advice, hacks, and so on. It even bleeds into print, I'd argue "PHP: The Good Parts" is the worst software engineering book I've ever read.
The Python and Ruby communities have their problems, for sure, but you're more likely to find good advice and altogether more competent people when asking for help there. There is a focus on constant improvement, elegance, and craftmanship while maintaining pragmatism in the Ruby community that fosters more of a joy for learning and building things than I think you'll find in PHP.
On the library side, I can't speak for Python, but my point with JRuby is that you have access to not only the Ruby ecosystem but the Java ecosystem. For the purposes of arguing the breadth of applications I can simply stop at the Java ecosystem, full stop, since it's arguably the largest set of libraries available on a single platform ever built. To start, just look at the Apache projects, Hadoop, Lucene, Solr, Mahout, and more give you access to state of the art machine learning, IR, and data analysis algorithms that are beyond your wildest dreams in PHP. And this, of course, is just the surface of what is available to you.