If you have Mac OS X 10.6.6 Snow Leopard or newer, and as Mac OS X 10.7 Lion is newer, you do not need OS X 10.8 Mountain Lion to get OS X 10.9 Mavericks. One could simply upgrade to OS X 10.8 Mountain Lion from Mac OS X 10.6 Snow Leopard, thus the same principle applies to OS X 10.9 Mavericks and Mac OS X 10.7 Lion.