I don\'t see what the fuss is about. Any bands who plays a significant amount of improvised music qualifies as a jam band.
This definition, does, of course, include a lot of music that some would consider jazz, or fusion, or bluegrass, or pop, or whatever, but in my mind improv is "jamming" and thus the band is a jam band. That is not all that they are, but it is one thing that can be used to describe them.