where do you draw the line between for instance "adventurous prog metal" and other genres anyway? genres are dumb. especially "prog metal".
I used to think genres were dumb, but the more music I listen to the more I realize that there are very real demarcations. When someone is influenced by or fits into a certain tradition, you just can't help but hear it all over. The difference, for example, between prog metal, neo prog, and modern retro-prog (whatever you want to call it) is usually just completely obvious to me after a few minutes of listening, for example. I would never mistake the stylings of an IQ for those of a Redemption or for those of a Magic Pie, for example - and these are genres that are very close to each other, and that most people would say are indistinguishable. If you're listening, anyway, they're clearly not.
Some bands straddle the line, but for all the protests bands give on being labelled by genres, I always wonder "then why do you play exactly within the confines of your genre if you don't want to be labelled as being part of that genre?" Genres are not bad or limiting - rather, without them, you lose the sense of historical development that bands go through. Dream Theater and Knight Area end up sounding on the surface very similar, such that they'd probably appeal to roughly the same people, but their historical influences are different, they come from different places, and it's written all over their music. If you just throw up your hands and say "genres are dumb," you'll miss that.
I also generally tend to think that the musicians people point out as being genre-defying and unique are actually far less so than people think, and that they usually say this because they haven't listened to enough music. It reminds me of a guy who once told me about the band Camel, and it became clear through the way he was describing them that he didn't know what progressive rock was - he thought that Camel was the only band that played anything remotely like their style of music, and so he thought they were some sort of stand-alone genius band. Clearly, no one who listened to Pink Floyd and Genesis would think anything similar. Genres are important because in music, history is important, far more important than the individual band or songwriter, although the bands and songwriters often hate to think that.
Inventiveness comes from working within your history to find new avenues for the music, and you can't do that without recognizing that history. That's what jazz is all about and when it's good, so is prog. Problem is a lot of the time prog just sort of sits still.