There are a few different variences of the ATX form factor like Micro-ATX and Flex-ATX. But the "Standard-ATX" should just be the "ATX" type. Don't hold me to this, but I am 99% sure that they are the same thing and they carry the same features like 20-pin power-supply connector, cooling condidtion standards, integrated I/O connectors, etc. Hopefully someone else can verify this for ya.
-Mike