That's the same analysis I've come up with as well, Ben. As an all-around weapon, I don't think there's one in the SM Codex as versatile as the Flamestorm Cannon. The way I play with LR's (usually) is moving them Cruising distance on turn 1 (sometimes up to turn 2, if I'm playing DOW), and then Combat after that.
With my LRC, I've very rarely ever had the chance to use it's Hurricane Bolters, and most of my opponents usually keep their models in cover if they realize the Hurricane Bolter can reach them. With a Flamestorm Cannon, I find that my opponents need to either come to me sooner (to disable my LRR or attack some other unit close to my deployment zone) since cover saves won't help him, or keep them further back away, to keep out of reach of the Flamestorm templates.
It's also the only weapon that's effective against (I'm estimating) at least 90% of all Infantry Troop types from all Codices. It kills horde armies like crazy, and is effective against all Power Armored MEQ's. Only army where I can see a LRR to be less effective would be against Tau, or any other army that is shooting intensive. Otherwise, as an all-comer's LR, I love it.