How many IRC networks could afford the hundreds of thousands of dollars it would require to run 10 - 20 NT servers running commercial software?
IRC networks tend to be a collection of servers donated by different companies. There's no one single network-wide budget. The budget is dependant only on the site that is hosting the server, which, mostly likely, are running Windows boxes. So that suggests to me that they certainly HAD an option to use Windows but didn't because of the Unix-like OS's greater reliability, security and dependability.
As for the $calc fault: mIRC is written in C/C++ (according to Khaled's FAQ) and C/C++ (like Turbo Pascal) has a limit on how high the value of an Integer can be. So I'd say that's a fault with the language itself, not the IRC client.
