Well, there's two ways to do that in Clojure: write your own list processing (usually regarded as bad style) or use reducers. Both are appropriate in specific instances, but the fact remains that the lazy seq code above is the idiomatic way of doing it in Clojure. So the _default_ way of doing it is slower than LINQ's default way of doing things.

It wouldn't be hard to make LINQ behave like Clojure, either.