I agree with you, and I was equally frustrated. I think the problem is that most people don't use the Math module that much. Hence they try to keep the Numeric classes smaller rather than filling them with all possible Math functions.

However, it doesn't take much to "fix" it the way you like it. You need to patch Numeric. Whenever you call a method that doesn't exist, it calls the method "method_missing". Hence you can monkey patch Numeric#method_missing to call the equivalent Math function.