Last time I checked it's a staged paywall. You get X articles for free without any action, X+Y articles if you register, there may be another "free" stage, and of course you can start paying and that may have more than one level.
They compete with The Wall Street Journal, which is famously about the only paper that made a success of on-line subscriptions a long time ago.
I guess they've changed their policy and I didn't notice because I registered a long time ago. Not a good idea, there should be no friction until you've tasted a bit of the fruit they're offering. Then again, such mechanisms tend to make it too easy to entirely circumvent the subscription system.
There is a recurring argument that these sorts of paywalls are okay for submissions because you can run various circumvention techniques that remove them. Aside from the serious legal grey area there (it may fall under the realm of "hacking"), it is in effect stealing for those of us who abide by intellectual property rights.
Sites that implement paywalls understand that they eschew social news sites as a consequence. Abide by that understanding.
A counterargument is that they have a registration wall that allows you to read a certain number of articles per month (currently 8 according to carbocation in another subthread of this thread). I find their content to be of sufficiently high quality I had no qualms about doing that some time ago.
