Yes, they artificially limit the reach of your posts, and then you pay them to get more exposure. You can also pay to have your posts more visible to particular demographics.

And of course that payment is on a sliding scale, and no amount of money is enough to reach all of your target audience, and it's also for a limited time window.

MOAR! (I didn't know that they already did charge them. But more is always an option in their vocabulary).