May be an issue of quality, it may not.
The reality of the situation is that the Hobie 17 hull is round on the bottom and when you put the round axle of the beach wheels under the hull, you create a severe point load situation since the weight of the hull is distributed over a very small area. If you push down on the boat or someone sits on it with the wheels under it, you up the stress on the hulls that much more. Hull cradles spread out the load over a much larger area and therefore minimize the potential for damage. They're definitely a worthwhile investment.
I'm not disagreeing with you at all - it's just my '87 was built like a tank. I never used cradles with it (many 1,000's of road miles and w/ Cat Trax) and never had a problem. After listening to this, I'm definitely going to be more careful with the new one. I've already been using cradles on the trailer (over 5,000 road miles since 8/07) - I'm going to be extra careful with the beach wheels.