It's the "instant ratings" problem. In years passed they needed a few months to see what ratings were. Now they know the next day, for every episode. That means they can cut them fast.
The other problem is more for the basic cable networks, and that's the "order and film them then air them a LOT later" syndrome. Network TV tends to work on "as needed" cycle (like Firefly) so you get maybe 3-4 eps made after the cancellation order is given. This means you tend not to get a finale, but also that seasons get cut short.
Then you have Caprica and SGU where the shows are done filming, then they start to air, and they may decide to cancel the series and there's no chance of having any closure.
The Jedi Master
The anteater is wearing the bagel because he's a reindeer princess. -- my 4 yr old daughter