Hi Steve
A North sail should not delaminate any more than any other, unless it is very old and has been left out in the sun? The WB sails are sometimes perceived to last longer because of their cross-cut construction which means the leach will stretch gradually over time as seams stretch and needle holes elongate, so any sinkage in the fabric will not be as obvious. However the designed shape is changing as the sail gets older, as all sails do! Unfortunately sails are a useable commodity that are only at their best for a year or so. The price is often more affected by exchange rates, I understand the WB sails in Euros are now more than a North sail in GPB.
The Olympic squad sailors are a good source of nearly new sails as they move them on after only a few weeks use and around 50% of the new price, although they are sadly a rarer number now due to the recent Olympic decision
Hope that helps
John