I'd say we would be getting into too many estimates and variables. A list could definitely be done, simply by adding up total album sales and total number of tickets sold over a bands career, but there are several problems with this.
1) Led Zep, Pink Floyd, and U2 will obviously be way ahead of new artist like Coldplay or Snow Patrol, as will dozens or more other artist simply because they have been around longer, so there is little purpose in making such comparisons except for those ALL TIME list.
2) There are many differences in the different decades of the music business. Back in the 1960s and 1970s, the population of was much smaller. The record buying public per capita was also much smaller then as well. Artist back then on average could not sell as many albums or tickets as the average artist can today. The otherside of that issue though is that these artist have been around longer of course and have had more time to sell albums over the years.
3) Many artist chose not to tour for years, or more than a decade, for reasons that had nothing to do with the business. In addition, tours back in the 1960s and 1970s were never on the same scale of average tours today. Tours back then had fewer shows and played to smaller venues usually. Consider the fact that the U2 will likely have sold more concert tickets on the Vertigo Tour (4.5 million) than Led Zep did during their entire career. Led Zep only played 13 shows in stadium sized venues during their entire career. They rarely toured after 1975 and then broke up in 1980. I don't have the exact figures, so that might be a slight exaggeration, but its not far off and it probably is correct.
Its far easier and very accurate to use "current tour sales/current album sales" as the basis for determining current popularity and that is the standard the industry uses. Also, if your no longer a band, then your no longer in the game obviously.
An All Time list can obviously be done, but obtaining all the figures and adjusting for changes in the business over the decades makes doing such a list difficult and leaves it open to lots of debate. Veteran artist would dominate the list simply because of the greater amount of time they have been in the business compared to younger artist.