Thanks for your replies,
I think the reason for not using Ribs is probably one of the following reasons:
1) About 60% of boat sales seem to be for fishing applications.
2) They like to build their boats like their cars, big, ugly and heavy.
3) Apart from a couple of months a year these guys experience fair weather boating.
At the Perth boat show i saw this interesting fast fisher, this is their version of a pontoon boat. The question why springs to mind?
Check it out but please do not laugh too hard.