This seems more like a sinuous function than an exponential one to me. Having more data would likely show a seasonal trend. Interestingly, it starts and finishes with the same value.
Yes this one is the most interesting to me. It's per capita, so it's not effected by changes in the number of registered players. I think you're right that it shows seasonal trends, such as increased activity in cold months (if you live in the northern hemisphere) and vice versa. It also shows that the diehards haven't been discouraged by the year long exodus.
