I would call it a religion and although they do not hold to the same belief systems as most Christains they none the less have things to learn about, and many find that they have workable means to a better life. They have a few movie stars that have promoted the idea that they have greatly benifited by those teachings and readings.
Perhaps mainstream religions just use the word "cult" for any religion they think is off the wall because it does not promote the same ideas they teach. The word cult sounds like occult and that sounds like something that is non-christian or even "evilish". Like a devils cult.
A cult is normally classed as a group that uses mind control methodologies to basically brainwash their following so they will not stray from the flock, they teach isolationism and often make people think that their parents and other relations are evil and should be avoided. They keep you as busy as possible from the time you get up til you go to bed - doing church stuff. They expect you to become totally dependant on the leader of the group and you often must give up your personal wealth to join, or donate it to the "cause". Always "the cause" which is most of the time has to do with preparing for a doomsday or the life here-after. They often employ a strong system of rewards and punishments. And sometimes they break the norms of sexual relationships.
Cults create mindless robots and zombies out of what otherwise would be a thinking person.
Where as our standard religions are both social events and they offer a time for worship or bible study.
So you work all week, deal with your family, hobbies and other entertainments. And once or twice a week you go to the church for a little inspiration, entertainment, and to learn about things in the Bible. So it is not a full time, all consuming addiction.
Although L Ron Hubbard is very intelligent and he might employ a few of the cult tricks at his gatherings he at least has something to offer. A science fiction writer, new ager and motivational speaker, he was able to tap into a new generation of people seeking a religion that seemed to offer more then what the normal churches were providing.
And so... religion yes, cult no - why insult thousands of people with such name-calling?
http://www.lronhubbard.org/ http://en.wikipedia.org/wiki/L._Ron_Hubbard