Some people are yet to grasp that nothing is free.
The amount people spent putting that server, developing the back end, managing the database etc is not free. In business terms if blizzard had to do the same it would be a reccurring cost that includes (incomplete)
server hardware
server maintenance
cost of running the server.
licenses for all software required to run the server, maintain it and add it to their datacenter monitoring.
cost of developing any upgrade
cost of fixing bugs, identifying them, testing them
cost of the x amount of people salaries you have to add + the extra cost depending on the country (national insurance, taxes, retirement etc).
etc etc
Some people think time = free. You will one day grow up and find out that time is not free and time is very very precious, for a company, time to do x is money that is spent. If money is spent, it better be a good investment that will allow the company to recup the costs.