The carriers must flex while travelling cross country. A carrier bolted together would never last as long, bolted. They would work loose at the joins unless each hole had been reamed as per Richards post.
Thats the structrual side.
Now for the asthetics. Rivets win by a country mile in every posible way. They are classic!!, with so much character!!!!.
(Sorry you T16 guys) I have a welded hull AOP, which was the only carrier I could find, while hunting for a riveted one.
Riveted bridges were still being built in the 1960's (Auckland harbour Bridge, built by a Japanese company)
I just love riveted structures.
I use the same legal defence as Shaun. Its my opinion (everybody has one)