That's a good general rule for all modern bikes, not just Triumphs. There are a few exceptions here & there, but almost all bikes with spoke wheels have inner tubes & almost all bikes with cast/forged/"mag"/one-piece wheels do not.
Just for some background... The 1980 Kawasaki KZ440 LTD I learned to ride on had one-piece wheels, but came from the factory with tubes. When I bought it 24 years later, it had tubeless tires & no tubes. By 1984, they were shipping the GPz550 without tubes. This has always made me think that tubeless rims were a late '70s thing, but tubeless tires were artificially expensive 'til the mid-'80s.