what do people define as metal these days? some people have writen sepultura, then others have writen led zeplin, seriously ***, sepultura is hard core metal, tool is metal (go tool) led zeplin is rock, don't mix the genre up, there's a lot of difference, but seriously you need to add tool to the list.
Early bands such as zep are really hard to classify, they had such a huge influence on the evolution of metal, so i think a lot of people tend to classify them as metal. i agree they're definately more rock but it's a very fine line with earlier bands such as zep, rainbow, etc etc.