Landlords don't make money by providing a service or selling goods. They make money by sitting on something no one else is allowed to have. They don't have to do anything more than sit back and collect checks. Sure, they bought the land originally, but there's no more investment to be made after that. They can invest in a nicer building or grounds, or compete on services such as "free" utilities or quicker repairs, but those are above and beyond the "rent-seeking" part of his revenue. He could just rent an empty lot, like a trailer park or campground.
This is analogous to, for example, telephone lines. They cost a lot to initially build out, but once they're there, the phone company only has to charge people for access. They provide a service back at the switching station, but most of what they're getting money for is owning lines that already exist. It's harder to separate rent from their other revenue, but it's there.
It generalizes to all revenue that is of the "sit back and collect checks" variety. Cellular carriers sitting on a chunk of spectrum they can sell access to. They can just rent it out to MVNOs if they don't want to provide those services themselves. Film studios sitting on a catalog of work they can sell, license, etc. So yes, IP revenues are definitely rents.