There aren't any DOS commands in mIRC, however the command-line format (which I assume is what you mean) is the entire basis of the IRC protocol. Things like Services and many user/channel modes are non-standard and cannot be implemented effectively as a GUI in the current implementations, they simply differ too much from server to server and not enough detailed information is provided for the clients to dynamically create a complete interface for them. Until that changes people will always need to know at least some of the commands for the servers they use.