"First of all, where I in Fitzgerald's place I'd do exactly what he did: arrest Roddy and try to stop him from selling a seat..."

Actually, by arresting him immediatly, before he could "sell" the Senate seat, Fitzgerald prevented gov. Blagojevich from committing a crime. Now, it can be said that he "just thinking about it", which is not a crime.

This allows the governor to step down and say he is sorry and go home a free man. Much less damage to the party that way.