[waddlesplash]

Haiku's "raison d'être" is to be a fully-fledged desktop operating system for general use. So, if there aren't native applications to fulfill daily tasks, then Linux ones tend to get ported.

Anyway, as for the question "why Haiku, if it's just ported Linux apps?" well, because Haiku is a much more cohesive system than any Linux distro. Even if every app you are running on it is from Linux (besides Tracker and Deskbar), the entire system underneath those applications remains tightly integrated.