But Queensryche was ALSO commercially successful, so what's the point? The difference is that Queensryche is currently unsuccessful after a decade and a half of declining sales while DT is still in the top 10 with nearly ever release and captured a market of younger adolescent kids, which Queensryche could never do anymore.
And getting into 'what constitutes a measure of success' is a redundant point. Nobody is saying success or failure have quantifiable lines in the sand - but if you're going to say Dream Theater failed commercially, I'm going to challenge that opinion and disagree.