My understanding is that the OS X EULA does not permit OS X to be run on non-Apple hardware or in a virtual machine that is not also running on Apple hardware.

My understanding is that the OS X EULA does not permit OS X to be run on non-Apple hardware or in a virtual machine that is not also running on Apple hardware. So if you want to test on OS X (including Safari) then you need at least one Mac. Sharing a single Mac for testing could be enough, but given a team of more than a few devs and it may become a bottleneck. You can run Windows and Linux VMs on a Mac - without breaching any EULAs. For web devs who care about Safari, Macs become almost mandatory. Note, I do not own or develop on a Mac. I primarily work on a desktop simulation software written in Java. I found the Mac love professed by other devs I know somewhat bewildering for a long time. I was only when I dabbled in some web development with a Rails app that I realised how much pain came from browser differences across platforms. Now the strong preference for Macs made more sense.