It's true boats would on first glance seem to have it worse that way. But all wood moves and changes in moisture content. No boats are subjected to 25% winter humidity and 90% summer humidity as a bow indoors can be every year, even here in Vermont, and even hanging from a wall. That represents a substantial movement range in the wood at the glue joint.
The Gougeon's pointed out that it is water vapor, not liquid water, that readily penetrates paints and finishes which are technically "waterproof" and affects the wood beneath. Not much stops vapor, the gaseous state of water. The most resistant finishes at the time against vapor penetration were epoxies and paraffin wax, which is why they coated planking with epoxy, and used extnsive lamination in racing boats and ice boats.
