Yes, when spending most of the day in front of a cross-platform IDE the OS has very little effect. But the OS has an effect on configuration side of things. Due to working in parallel with different projects and systems I need to have multiple versions of JDK available, a set of multiple build tools in different versions and multiple application servers. I have used Windows, OSX and Linux for development and Linux has been the easiest environment to set up and maintain and Linux VMs also solve the multiple app servers-problem. I don't have that much experience with OSX (only got my MacBook Pro a couple of months ago) and so far it feels quite alien. While there's the familiar power of Unix lurking in the back the GUI side feels very cumbersome and something I feel I have very little control on. Is that the Apple usability magic that people usually talk about?
Say you are a Java (it's easy, common, and cross platform) developer this means you need your Eclipse/Netbeans IDE, a JVM and or some Java based web server. So you have your IDE+JVM on the OS, and development/deployment & test environment on a virtual machine, does it really matter to you if you are running Linux, Windows or OSX in this case? All you use and see is Eclipse, a text editor, Virtual Box and a web browser.