PHP exists to script web pages. It’s been expanded to allow you do a lot of stuff from other application layers, but it basically still serves that one layer. A key advantage is that it has a nice, shallow learning curve. And, as the backbone of Joomla, Drupal, etc., it ain’t going anywhere any time soon.
Perl is the former language of choice for doing some of the nitty-gritty web-development tasks that PHP isn’t particularly well suited for, but it was never terribly good for scripting web pages; it’s very easy to build highly idiosyncratic code which is undecipherable to all but the top programmers. Essentially, once you convince someone to allow you to develop a system in Perl, you have a job for life. And a lot of users of such code don’t exactly enjoy that feature.
Python is replacing Perl, but it also does what PHP does easily enough that there seems little reason to use both Python and PHP for one enterprise... except the vast arrays of PHP creations.
This, like "I could care less" instead of "I couldn't care less." is said by people all the time and is actually the opposite of what you mean.
The learning curve is a graph of knowledge acquired vs. time. A "nice" learning curve is steep. A shallow learning curve means you've have been working a very long time and have not acquired very much knowledge.
Tonight's Pedantic MomementTM has been broguht to you by Bristol-Meyers.
I am a big fan of Apache Wicket to develop Java-based web apps....I can build my HTML file and get all of the CSS goodness worked out in any HTML design app, then code the matching Java class to pop the data onto the page. Writing reusable components is a snap. And it really works well with toolkits, like Twitter Bootstrap.