1. They have CORE Haskell contributors on their payroll to deliver this type of project (what this mean is that no... Haskell isn't any better than other language, it's just that they have people who know Haskell very very deep to the compiler level...)
2. In-house custom language eventually does not scale (the EOL is much much much shorter than other programming languages), plan for that :)
This is just complete snark, that misunderstands the general thesis of the article (intentionally?).
Having a core language writer on your team by no means implies that the language in itself is unusable without the designer himself. Your comment explicitly mentions this, and you could really generalise this to any language at all.
The fact that they hired a haskell contributor over a PHP or Ruby contributor was perhaps something you should consider. Or, you know, you read the article, where they answer some of these basic assumptions.
This is extremely presumptuous for a parenthetical. If this is what you believe it merits a comment all to itself, because I don't see how this follows in the least. To rephrase what you're claiming: if a language has a flaw than it can not be any better than any other language.
Who should they hire instead? Given the opportunity and the means, wouldn't you hire someone of that caliber for your preferred language/environment?