You can just as easily say RoR is slower (than, say, Symfony 2.0 on PHP with an opcode cache) and harder to work with (from a system administration perspective).
Take a look down the top 100 website list, and of those sites that are web applications, more of them will be built on PHP than not. I don't think there's even a Ruby application among the top 100 sites except parts of Twitter, but I could be forgetting something.
- Yahoo! (Answers, Bookmarks, Delicious, etc)
- WordPress (.com application is #19, another 14 million active installs of the free software)
It may not be cool right now, but it's certainly practical.
The problem with this argument is that all of the websites that you mentioned were founded before Ror or alternatives were mature enough. Adam D'Angelo (former CTO of Facebook) said that if Facebook was created now, they would not use PHP (source: http://www.facebook.com/note.php?note_id=137376312958147). I can imagine that the situation is similar with the other websites.
It's extremely important to draw a distinction between cool and practical. HN is all about the cool new hotness. People here are always on the bleeding edge of technology, so they tend to flock towards those instead.
Also, hiring PHP developers is easier than <insert cool technology here> developers. There are just more people with PHP knowledge. Not saying that is a good reason to use a language, but it is a factor.
But when it comes to hiring _good_ developers, Python/Ruby/Lisp are definitely a better option.
In my experience, while it seemed at first that hiring PHP developers would be easier, it actually proved wrong, as we had to spend way more time to find _good_ developers among the mass than we would have if we were looking for, says, Python developers.
My personal opinion about this is that the better/more driven/valuable developers are the ones who are quick to try new tech and follow emerging trends. Many people know PHP, but I think you'd likely find better talent in the long run if you offer a position that uses a more exciting back-end.
I'm in webdevelopment many years now and switching from php to ruby was a step I'll never regret. About the sysadmin perspective, I manage all my servers myself, used debian on my workdesk long enough to do this, and in the last year with all the stuff like bundler and the new rubygems.org it got so much easier. If you need it even more easier then Heroku is something you won't get elsewhere.
I like Kohana much more than CI, if only for tossing PHP4 support.
However, but I've found that there is lots of fragmenting in the community/documentation. See the differences between 2.3.4 -> 2.4 (lots of breaking changes) -> 3.0 (almost entirely different framework). Which is kind of a bummer when using it for long-life projects (we have a few projects are stuck on 2.3.4).
That said - Symfony 2.0 looks fantastic, and very much like the next "Rails-like" PHP framework.
Exactly the same story here. Our primary product is stuck on Kohana 2.3.4 because of the lack of care that the Kohana team put into backwards compatibility. I wouldn't be surprised if they decide to essentially rewrite things again in the future either. If I could go back in time, I'd pick something else.
Kohana 2 was "just a php5 fork of CI", while Kohana 3 is practically a whole new framework. The "problem" is that Kohana team doesn't like handicaping new versions for sake of complete backward compatibility.
They just make the framework better with every new version, although in case of Ko3 minor versions are backward compatible (for example 3.0.8 with 3.0.1., but 3.1.0 will not be, at least concerning the response object and the ORM logics).