I think this discussion would be missing something if John Paul Jones was not mentioned.
John Paul Jones was a master muscian formally trained and a multi-instrumentalist; probably most well known for playing bass, all sorts of keyboards, and a huge variety of styles of mandolins.
He received a lot of respect from Led Zepellin fans and was an impressive showman and very groovy player on stage. He was also, and still is, a major producer and muscian, playing with many bands and having his own band at present.
I listened to the first Led Zep cd a couple nights ago at night when everything was quiet and my mind was clear and free of preoccupation. Unaware of this thread, JPJ's bass and keyboard contributions on the cd struck me as very essential in the up front sound of the interwoven music of the players. He was totally grooving with the drummer but also was heard to move to stand out beautifully in so many songs, while Page laid back; as well as hitting it along with Page of course.
I also was turned on by the way he played the keyboards, evidently using bass pedals to give the keyboard parts a distinctly basslike affect. Listening to his keyboard playing I heard melodies that seemed to dip into the well of his background of serious symphonic music, hinting at the ambience of sound in a cathedral, etc. This keyboard playing in Led Zepellin may also be something that is not noticed sometimes, but, to me, is awesome.
I personally think that most Zep fans would greatly miss JPJ if he was ever replaced in the band; similar to how many of us Stones fans feel that something is missing from their music since Bill Wyman retired - the new bass player does not impart that same vibe to the music.
I think there are some bass players that have earned the respect of the fans of many bands, including, also, The Who and the incomparable John Entwhistle.
Also, I don't know if the fans knew it or not, but many great muscians like, as stated earlier, Albert Collins relied strongly on their bass players and had great respect for them. But this goes along with the thinking that in general bass players contributions are commonly appreciated by other muscians most.
Also I think it is true that in some bands bass players are relegated to minor roles hidden in the background. On the other hand great muscians like BB King and Stevie Ray Vaughn would often feature each member of their bands in live performances, giving them time to feature some awesome lead solo's for the benefit of the audience, reinforcing publicly that they didn't produce their awesome performance alone.