Why is Mollom a web service and not a stand-alone module?
Mollom’s intelligent filter technologies learn from the spam information gathered on all sites using Mollom. This means that if another site gets spam, Mollom learns from it and protects your site better if that spam-wave rolls over you. Mollom uses so-called "crowd sourcing" or "community intelligence." The more users using Mollom, the better its performance and the faster it can learn. A stand-alone module could never achieve this.