You're only eligible to be nominated 25 or more years after your first album was released. The first Led Zep album was 1969. Add 25 and that's 1994, thus making '95 the first year they could really get in (depending on what time of year they do this thing).
I loled because one guy is a sometimes editor of the Rolling Stones and another complains about them not being a "big enough name", ie pop.
They do have a category for musicians who're not rock'n'roll but do work in genres that led up to rock, such as the blues. Most of the artists that were inducted through that category did most, if not all, of their work before rock kicked off in the 60s.
I still think the RnR Hall of Fame (or any "Hall of Fame") is a self-adulating stroke of arrogance to fulfill the need to be "accepted and/or recognized"; Also known as an "ego trip". Just like any award... Hypothetically, I would care less if I had gotten into the Hall of Fame, so long as my bandmates are cool, my family's proud and my friends and fans enjoy.