It's a different, weaker level of type safety that's become so prevalent that you probably take it for granted. The runtime checking is just to make sure that operations are performed on logical types.
My favorite analogy for this is the restaurant one. Haskell insists on having two waiters: one to deliver the food and a second to deliver the check. Clojure allows one waiter to deliver both, but throws a fit and leaves the restaurant if the check arrives before the bill. Assembler eats the first thing that arrives and signs the second, even if the bill comes before the food.
Clojure is "type-safe" in that it will exit instead of performing an illogical action (e.g. dividing a string pointer by a network socket). It's just as type-safe as Haskell code littered with fromJust.
What you're talking about now is totality. Both Haskell and Clojure allow non-total functions (functions which may not return a result) - the checking that they do are to stop undefined results. Agda is an example of a language that only allows total functions.
Adding the fromJust Haskell argument seems to have confused the argument I was trying to make. I had two points. The first one was better expressed by Evbn and I don't really have anything to add to that.
The second was that Clojure arguably has a type system. There is exactly one type, Stuff. Every function takes Stuff and returns Stuff. Of course, functions themselves are a kind of Stuff. Now, it lacks totality, but otherwise every compiled Clojure program has passed the type checker. It's just that type checking is a no-op, since there's no way for anything to have the wrong type.
Totality is different. In C you can (using a pointed cast cast) add a float to an intended and get gobbledygook (by interpreting the bits in memory incorrectly) and keep going. In Closure you can't, it will throw an exception, but you won't get warned about that until runtime.
My favorite analogy for this is the restaurant one. Haskell insists on having two waiters: one to deliver the food and a second to deliver the check. Clojure allows one waiter to deliver both, but throws a fit and leaves the restaurant if the check arrives before the bill. Assembler eats the first thing that arrives and signs the second, even if the bill comes before the food.
Clojure is "type-safe" in that it will exit instead of performing an illogical action (e.g. dividing a string pointer by a network socket). It's just as type-safe as Haskell code littered with fromJust.