Well... considering I'll queue up Zeppelin often, and the Beatles rarely....
I probably heard Zeppelin in the 70's too... but I don't remember any of it, I was born in '78.
And when thinking "all time"... I have to agree. I can think of several bands with songs, even a fair number of songs that I'd rank up there with Zeppelin music, but very few that can do it over and over and over. Just get Remasters... two CDs, and every damn track I could listen to repeatedly (except maybe "Stairway...", I overdosed when I first started learning to play the guitar).
Then again... I know of one large group of people who would disagree with you, and all of this. *glances around, looking for Deadheads burning bud-laden torches, calling for the spirit of Jerry Garcia to curse us*
So... favorite Zeppelin tune, anyone? I can't decide... and would probably say the top three are "Since I've Been Lovin' You", "Trampled Under Foot", and "The Battle of Evermore". Damn you... now I have to crank up WinAmp and get the Led out. Oh crap... I just realized "Nobody's Fault but Mine" (gotta love the harp in that) wasn't in that list... um... can I have a top 4?
And, I play an MMO where I quote a bit of "The Immigrant Song". It fit sooooo damn well. It's a space based game, developed by a company in Iceland, and when I added it the corporation I run moved from safe empire space to the fringe low-security areas, risking conflicts with pirates (NPC and player types) to stake out a home with rich asteroid fields... and of course this embroiled us in the Great Northern War, helping to defend the Deklein region from the Phoenix Alliance, then the Band of Brothers, and since various other factions.
We come from the land of the ice and snow,
From the midnight sun to the hot springs blow.
Hammer of the gods will drive our ships to new lands,
To fight the hordes, sing and cry, "Valhalla I am coming".