-- Last Updated: Oct-04-12 11:10 AM EST --
Kayak models are like women clothing. It's dictated by fashion not function.
By "fashion", I mean it's by what people THINK they "want". Therefore, not necessary what a boat can be made to do.
In terms of function, your list is complete:
- a well rounded expedition boat
- a fast day tourer
- a playful, surf-able (short'ish) "fun" boat.
In reality, there're many "in-between" designs: expedition boat that are playful, expedition boat that leans towards going straight and fast, etc... Because that's what people WANT!
To be fair, for people who only have 1 boat (or even 2 boats), we're already going down the "compromise" path. So someone who want a day boat that can double for mini-expedition do "want" something between the first and second of that list. And the list goes on...
(I myself is guilty of that "compromise": what I paddle fits into 2 categories: a playful one and a fast day tourer. But I only have storage space for one boat: so instead, I got a reasonably playful boat that has decent speed. I even camp out of it too! It's a good compromise boat for me but it's a "in-between" design)