The whole relationship between Zynga and Facebook is interesting. FB generates 10% of its revenue from Zynga, but yet they are constantly implementing new restrictions on "game spam" which directly hurts Zynga's sales which has some pretty solid numbers supporting the more "spammy" a game is, the higher its install base and the more revenue it tends to generate.
FB might just be trying to get ahead of the bubble burst though. Why annoy a large number of your users, to the point of deactivating their accounts, just to help boost a fad in Zynga's titles? Better to sacrifice a little revenue now in order to cut back on account deactivation and build a better relationship with the user and more stable revenue down the road.
As it has been shown by the failure of their own website service, Zynga needs FB. FB doesn't need Zynga. Zynga's main goal is to shake that platform dependence now, but it only seems to know how to make games that rely on the FB model as its iPhone titles have been fairly weak in comparison.