Is operating systems really matter for developer?

Answer 1

Yes. Of course it depends on what you want to develop.

Answer 2

Well, in most cases if you want to build something that's compatible with a specific OS you'll need to test on that OS. Mac/iOS in particular actually require the use of a Mac to build apps made using Objective-C. All of the OS's also have plenty of differences that can cause incompatibility in programs ranging from file system structure to bugs in the OS itself, not to mention line endings (\r\n on Windows, \n on Linux & Mac) and bugs in the program's that run our programs.