It's a language specifically designed to make it very difficult to do anything interesting.
PHP (the language, not the implementation) has some very deep problems, in my opinion. But at least you can sketch out a rough solution, and gradually turn it into something more polished.
I think the best design is done by coding little sketches that gradually become more and more complete, and are cheap enough to throw away; not by drawing complex UML diagrams and then carefully casting them into perfect code. That's just impossible, and the result is a lot of bloated crap that is very difficult to change when (inevitably) your design changes.
Writing AdSense or GMail in Ruby/Python/PHP will force you to pay the "tax" later on and the tax will be huge before you know it. You'll end up with a scratch re-write like it or not.
I'm not sure what you're trying to say here. Is the "tax" the upfront cost of writing code that uses static typing? If so, I most strongly disagree.
Static typing is not a silver bullet. The claim that not using a static typed language for anything complex will result in a "scratch rewrite" is absurd.
;P