I have not seen a printed Swiss Travel Pass yet this year, since we're no longer processing the orders in this office.
1) Standard practice on most rail passes is that there is a blank spot for the passport number, which is filled in by the agent who activates that pass in the station.
2) When a pass is pre-activated with start and end dates, as all Swiss Travel Passes now are, then you normally fill in the passport number yourself, again on the line provided.
3) If there's not even a blank spot to fill in the passport number (near your name), then it must be correct that it's not required. You may still be asked by a conductor to show your passport as ID, but then they'd just look for a name match.
It sounds like you received a printed pass, rather than an e-ticketed version (an option for the consecutive-day versions), which may account for some differences. Or maybe you will find it in small print, as another commenter mentioned.