It's like being responsible for some major development in iPhone5 at Apple and then going to a store and paying for all the marketing, productions costs by actually buying one.
So I'm wondering - is this mechanism some "Hollywood Accounting" where a band can run a tour at an ostensible loss while paying themselves through a royalties channel? Is it normal to split revenue this way?
Whilst there's a lot of Hollywood Accounting going on in the music business, I don't think this is the case here.
Firstly, publishing rights aren't always owned by the band themselves. The most famous example of this is probably The Beatles' publishing rights, which were bought by Michael Jackson, and then Sony. Every time Paul McCartney plays a Beatles' song live in his concerts he's going to have to pay some money to Sony, even though he co-wrote it!
Bands that do own publishing rights typically set up a limited company to administer them, and songs are frequently co-written. Bands are often obliged by these various agreements to effectively pay themselves (minus the administration cut, etc). The article linked to seems to suggest that Led Zeppelin either co-own the rights with Warner-Chappell, or have them administer them on their behalf. Either way, they'll want their appropriate cut!
The lady that has bought the stairway some time before 1971 must be a very wealthy person now. I wonder how much would that bustle from her hedgerow net on Sothebis today.
They have to pay themselves royalties for their own songs? Must be nice to be the middleman in that deal.