actually it's in the "drivers" page, not system list page
As of version 0.141, MESS supports 534 unique systems with 1,411 total system variations and is growing all the time (you can find a complete list of the supported systems here). However, not all of the systems in MESS are functional: check the specific driver pages to know the emulation status of your favorite machine in MESS.
if you click on "here" you get the list of supported systems which has no duplications (but I have to update that list... I will do it hopefully later today), if you click on "driver" OTOH, you get a list full of duplicate links to the driver pages. the latter is the page you are referring to, right?
last I heard, Duke was still working on a way better page, but I have no idea if he completed that or not... for sure it's not on the main wiki...