Oct 6, 2016 - 6:44 AM
Hi Jindydi, welcome to myswissalps.com!
Indeed, part of the Glacier Express route, including Visp to Zermatt, is not fully covered. You'll get a 25% discount. You'll pay CHF 27 one way for that leg. Further details are here:
I don't know why some passes include more than others. The Swiss Travel Pass, for example, includes all trains, boats, buses, some cableways and many museums. Eurail passes are mainly for trains: no buses, no museums, and some trains are an exception.