At Jon Walpole’s excellent site
http://www.cse.ogi.edu/~walpole/kayaking.html I was struck by the fact
that most of the boats in the photo gallery have upturned ends and no
rudder. These are the obvious (to me) visual attributes. I think a
couple of additional attributes are a tendency, on average, toward more
rocker and lower deck, than the American designs. I would have referred
to this as the Greenland design until Brian corrected me. Maybe the
better term is British design.

British, American, Greenland, Alaskan - it's really all so much semantics.
Generically speaking most people tend to refer to kayaks with fine ends, over
hanging ends or upswept ends as a Greenland design. As for what exactly
constitutes a true Greenland or Alaskan design is something that I don't think
even the purists can agree on.
Why the group to which you refer is primarily (or exclusively) using
"Greenland" design boats without rudders is anybody's guess. In fact, if you
asked each member of the group that very question you would be likely to get a
different answer out of each one of them. I have paddled many of the same areas
portrayed on Jon Walpole's site in more Alaskan type boats - Pacific Water
Sports Seal and Mariner's Coaster, simply because that's what was available. I
had a great time!
I will go out on a limb here (no surprise there :-) and say that the
majority of boats available recreationally today seem lean heavily towards the
Greenland influence. I believe this is more a result of marketing then anything
else. That stodgy bunch of die hard traditionalists in the United Kingdom from
which we get the BCU has always favored this type of boat. I have heard it
suggested that this is the result of their closer proximity to Greenland, then
to Alaska, more then any other particular reason. Whether or not this is true I
cannot say with any certainly.
While beauty is in the eye of the beholder, I think most people will agree
that Greenland style boats look sexier then their Alaskan cousins. I also feel
that the finer ends allow for a bit smoother ride. I have to believe that more
people choose kayaks (and cars for that matter) based more on appearance then
performance. There's nothing wrong with that! Some other reasons a person might
chose a particular boat would include the price, the color (don't laugh, it's
true), their buddy uses one and likes it, their instructor uses one, some high
profile paddler endorses it, it's easier to do bracing and rolling in for
people who do not have a strong brace or roll, and every once in a long while
because of performance in the type of paddling one intends to actually do in
that boat.
Very few of us are ever actually going to paddle from California to Hawaii,
or circumnavigate New Zealand. So choosing a boat for that purpose is really
kinda pretentious and silly. You should try a number of different boats and try
to choose one that you like - for whatever reasons happen to be important to
you - and enjoy!

Scott
So.Cal.