I think that's a bit apples and oranges. Arc is a long-term project that pg has said doesn't actually "have" to be useful to anyone anytime soon. Clojure, on the other hand, is under active, public development, as swannodette points out.
I think you might be missing fogus's point to a certain degree. His point is that active, public development for a language might not necessarily mean that the language designer is keeping contact every day. You might only receive periodic updates.
I don't see cookies being all that different from Arc in that respect. Cookies doesn't have to be useful anytime soon either because, well, it is useful already.