I suspect that the marketplace still has a little bit of an inherent cost. That said it is in a weird sort of zombie state nowadays. Demos for games you cannot buy, loads of apps that have had their API's move on many years ago. Internet Explorer! No with out of date SSL certs. A lot of title no longer available due to licensing issues.

For both Xbox 360 and Ps3 I suspect a decent business move would be to have a one time deal. A $100 (or whatever) one time payment that ensures that the core system will remain online for a decade. Doesn't mean any additional purchases but means that match making and friends lists will stay running until 2034. That would have given these systems a 26-27 year life time. Sony is still releasing system updates once a year to keep the Blu-ray keys up to date.