No, I'm not assuming, I've experienced it first hand. The language is ridiculous. I'm not going to rehash the tons of reasons the language is not technically sound, if you wish to believe it's a suitable language then go ahead. When a better designed language actually focuses on this space the different in maintainability will become measurably clear.
PHP might create a mess that is expenesive to maintain for _you_. It might even create a mess for a lot of people, especially newbies. Likewise with Perl.
That doesn't mean that creating maintainable PHP software can't be done - it's actually been done many times. While I agree that languages can make a big difference in maintainability, please stop blaming a programming language for your own mistakes.