Ok, I'll admit, this may sound a bit trollish, but if PHP is not one of the worst languages, then what languages do you rank below PHP? C comes to mind, not as a bad language itself, but lack of web libraries, but that's about it.
* Java has a really repetitive syntax, but it's libraries might make up for that.
* C++ with all it's features has bazillion ways to shoot yourself, but it's arguably fast and the syntax is bearable.
But php has both an ugly syntax, horrendous stdlib, and fame of security issues.
Maybe COBOL or MUMPS could be worse than php... haven't used these though.
Your "worst" is probably ill-defined: C is bad for web programming, but is certainly an elegant language and pretty good in its niche.
To me, both are effective at the tasks I need them to accomplish.
Is Instapaper merely adequate, or is it better? Would it have been that much better if it was constructed in Rails?
IIRC, Instapaper's a PHP application. I could have mentioned a larger site, but Instapaper was probably a better example, since it's quite popular with HNers.
But yes, it would probably be more easily maintainable if written in a better language, and the developers would be able to add new features more quickly.
To comment based on your metaphor, the problem is not that the screwdriver/hammer is ugly. It's that the grip doesn't feel right and it's unbalanced. You can turn the screw and drive the nail, but it takes more effort and might leave your hands scraped up.