What's the benefit the bank gets on offering me to pay my water/electricity/gas with credit card? It says "get extra 40 days to pay your bills" with no interest!

Is it just based on the statistics that people will eventually forget paying and then charge interests from those 40 days, or are there any other things they must be considering to offer this kind of service with no interest?
From a marketing point of view it's a very effective way of acquiring customers.

And you raise a good point, people often do forget these things, so banks can also profit that way.