Led Zep & disco!?

I've been a Led Zeppelin fan for a long time. I have all of their cd's except CODA. I think my favorite cd is Physical Graffiti, but I enjoy them all. I didn't know about Led Zep's existence as a kid, since by the time I was born the band had existed for two years. A friend of mine who is about 12 years older than me was a huge fan. As the band became more popular, however, he liked them less. He felt like they moved away from their roots, and caved in to popular demand, and when you listen to their music after the 4th CD (the one with Stairway), you can hear how some of the beats are more dance-able, almost disco-ish. I know disco had affected other bands, like Kiss and even the Rolling Stones, but it was so obvious with them. I'll try to find some specific samples, but listen to Houses of the Holy & Physical Graffiti - I'm sure you'll find a dance beat.