So Facebook put its thumb on the scale and started increasing the visibility of external links in the feed.
On your marks. Get set. Go. The fourth Facebook goldrush just started.
Jeremy Liew

Should clarify that this was catalyzed by the frenzy integration of Facebook Connect, Facebook Share/Likes and Facebook Pages.

There was literally an arms race to get the most Fans as possible complemented by a swelling ecosystem of like-gating and selling fake fans.