The Legion of Super-Heroes was the *first* group of heroes in comics history, ever. They pre-date the Justice League by about three months, and if one argues that the Justice Society of America came first with their run in All-Star Comics, well...they weren't really a super-hero team, they had individual stories that they told at a meeting either at the end of the tale or at its beginning.
The cancellation of the title has been a whisper on the wind for a while now, and to be honest, given the state of sales, the current economy, and other factors, perhaps the time is right to cancel the title now. Ironically, the Legion title will end during the 50th Anniversary year of the Legion of Super-Heroes, and with issue #50. DC Comics has futzed around with the Legion since the original Crisis on Infinite Earths, although the best effort to rectify the mess was during the reboot after Zero Hour, when the company restarted the Legion comics from the beginning of their founding, in an attempt to update the heroes for the current time. That alienated many of the long-term LSH readers, and well...now the rest is history.
A lot is going to be made about the cancellation of the Legion title over the next few weeks and months. As noted in various places, the Legion has had low sales levels for years now, and to be honest, but I don't believe this cancellation of the title is the end of the LSH. The Legion of Super-Heroes is a valuable DC Comics trademark and line, and the group will be back as long as DC wants to keep the ownership and rights to the super-hero team that started it all.
However, I think that what bothers me the most about this news is that Jim Shooter's big story arc was due to end with Legion #54. So what harm would it have been to let the series go and complete the story arc? Now we'll just get a half-assed job of wrapping up the story in less issues, and that can't be good. :(
So, what can I say?
Long Live the Legion!! :)