There is a geographical divide in Zep appreciation. Zep - on the behest of Peter Grant - focused early on crisscrossing the US, they did comparatively little in Mainland Europe. That showed, Zep were of course also big in Europe, but they were never HUGE like in the US. In places like Germany, France, Italy and Scandinavia, Zep in 1972 probably had a status like, say, Black Sabbath, but they were not in the peak echelons of popularity and sales like DP or even Uriah Heep. You just didn’t see or hear (radio) them often enough in Continental Europe.
It’s often forgotten, but in 1973 DP outsold all other rock bands in the US too - including Zep, Floyd, Grand Funk Railroad and the Stones.
