A significant difference is that when Eduardo took a dive he was acting as an individual, and there was no direct involvement by anyone else in the club. (Which doesn't mean there may not have been an indirect involvement through a pattern of tolerating and even encouraging this kind of cheating by players.)

The Harlequins foul was a lot more elaborate and was far more directly linked to the club as an organisation. The director evidently supplied the fake blood capsule and instructed the player to use it, and the club's doctor using a scalpel to produce a real wound in an attempt to cover up.

I think Dean Richards got off extremely lightly. A lifetime ban wuld have been quite appropriate.