Many newer sites are using PHP as well. PHP is used on established sites, but that just means that it's a proven concept. I also see many more jobs for php developers than Ruby (I have seen a few startups using ruby).
"You probably won't learn very good programming practices on your own - PHP has been pretty notorious for this, but maybe this has changed with PHP5, I haven't been keeping up."
I suppose this is true. But I think you can pickup good programming practices in any language.
Another reason to learn php is because it uses a C-style syntax, which will make it much easier to transition to other languages like c/c++/javascript/c#/Java.
Ruby uses a syntax all its own that you can pretty much only use in Ruby.
I also don't feel people should be learning a programming language through frameworks. It's like learning how to add and subtract using a calculator.
What beginners need to learn is programming concepts that they can use in any language.