I have looked at the past n similar products and it was always the same story. At some point, you don't need to look at the implementation details anymore, you can take this from first principles: somebody somewhere is running a ledger. You have to pay this someone one way or another, unless they're just volunteering.

> a few releases back they solved this issue

How are they getting paid?

Regarding the ledger operators, from https://nano.org/faq#nodes:

> Instead, participants on the nano network are driven by external incentives, such as helping maintain an instant payment network they can use without fees.

So it does look like volunteering / donating computing resources, and the 0 transaction fee doesn't reflect the actual costs.