They're doing it wrong. There are many successful, profitable companies making open source products with a subset of the features that their commercial offerings have. These guys are intentionally crippling the open source offering. It's practically a bait and switch.

The right way is to release an open source product that is full-featured and robust, and upsell things like support, managed hosting, and the kind of plugins and addons that primarily appeal to enterprise customers (although increasingly the latter are indistinguishable from advanced small users).