So many good points here it's hard to figure out where to begin to reply. Let's start with Peter Grant. He revolutionized the business end of rock and roll by making sure the bands and musicians got rich. This wasn't always the case, especially in a band's club days, Zeppelin no exception. Until Peter Grant entered the picture. Led Zeppelin never got ripped off by a promoter again and it also allowed them to concentrate on what they did best. Music.
Grant didn't stop there, or with the hit single vs album deal. He did not allow his band to be shown on Midnight Special, Don Kirschner, those kind of shows. If you wanted to see Zeppelin you were going to shell out $$$ to see one of their concerts. Or buy the albums. Or pay for "The Song Remains The Same" MTV was born a year after their demise. It would have been interesting to see if they would have done videos.
I was specifically talking "Houses of the Holy" when I talked about limited blues. One, two and Zoso are loaded with blues based songs. Folk song like "Gallow's Pole" and "Battle of Nevermore" are among their best. My all-time favorite Zeppelin is probably "Immigrant Song"
You mentioned that you wished fans would give some of their less exposed songs a chance. Absolutey true and I would say the same about Nirvana. Cobain's obscurities and B-sides are a treasure trove of wild riffs, melodic riffs, moody midtempo songs, tearjerkers, even Leadbelly covers. His version of Lead belly's "Where Did You Sleep Last Night" is absolutely chilling, especially after we learned of Kurt's fate. Mark Lanegan of Screaming Trees, with Kurt's help, does an even more frightening version of that song. People who only know Nirvana for "Teen Spirit" and "Come As You Are" would be pleasantly surprised.
There is a lot to listen out there gang. Sometimes you have to open your eyes to open your ears. And like Die Hard says, the correct stereophonic equipment doesn't hurt, either.