Commercial printers at the low volume end ( the biggest part of the market, the printer doing under 5000 pages a month) are very profitable, as the cartridge generally will do under 2000 pages. They also state in the small print the "new" part you just bought at full price might in actual fact be a refurbished cartridge from this program. I just have them refilled locally, which is around 30% of the wholesale cost ( or 20% of the retail cost) of the cartridge.
They also have a large profit from leasing the mid range printers and multifunction devices, where they use a refilled cartridge exclusively, though they do it themselves, and where they charge per page and per month for the machines. They rely on the design being such that the machines will give almost zero troubles (aside from user caused ones, which are charged for) for the lease period, and the machine pays off it's cost in the first year of the lease.