BVS
Blue Crack Supplier
To your second point, I agree about influence but why should commerical success be considered so heavily? There are examples in so many different artistic, athletic and scientific fields where a person was not a success but had a major effect or only gained fame long after their work. Music is no different. Also, where must the artist be commerically successful? Many artists are huge in certain countries but rarely known in others. Take Kraftwerk for example. They are not widely known by the mainstream music fan in the United States but they were popular elsewhere. It could be argued that they are one of the top ten, maybe top five, most influential artists of the last 40 years. Should their lack of commerical success trump that level of influence?
Sports and science can be "measured" to a certain degree. You can't measure music, but you can try and gauge it's impact and one of the ways is how many people were interested in their music, i.e. commercial success. It's not a perfect science, but it needs to be considered.
Nickelback have tons of commercial success but I think maybe 2 bands might list them as an influence 10 years from now, so they should never be considered. And on the other hand Scott Walker may have influenced musicians but how many households can list three songs of his? If an artist sings in the forest and no one is around, did they really exist?
Commercial success shouldn't matter to the listener, but if you're creating a Hall of Fame then it should be considered. I think the balance matters in that realm.