I never thought about that, but you have a good point. All they need is a waterproof and dustproof case, and the iPad will actually work!
One great thing is the iPad's PDF capabilities. Instead of carrying around all those huge, large-format blueprints, they can load it all on their iPad, and see it in an 8x11 size! With all the details!
Or they could zoom in, and see little parts of their prints by scanning and panning across it! If there is any problem, they can simply take a picture of of the jobsite, and superimpose it onto the blueprints to show the difference!
I think that contractors and gardeners could make great use of the iPad! You could put a set of plans for a whole skyscraper on it!