The rims you cited are 700c, and not the stock 650A (26 x 1-3/8 EA3). 700c wheels can be used on a bike like this, but need replacement, short-reach calipers and very likely removing the fenders, unless he opts for undersized, 28-32mm tires. A standard tire today is in the 35-40mm range for these. Some people don't want to do that.
At the relatively modest spoke tensions for these wheels, a decent pinned rim like the CR 18 is fine and offers no real loss compared to a welded rim. These are relatively low-tension wheels on vintage bikes that most people ride on the road rather than in high-impact uses. Pinned rims are a liability in off-road riding where debris can split the rim joint, but I doubt he is doing that with a 60+ year old Rudge 3 speed. He's paying an awful lot more for rims where the return on that extra money is of marginal use.