TO's act was disgusting no two ways about it, and there is no excuse or justification for what he did.
Having said that, suspending him for spitting on a player would be excessive, IMO.
Players are generally suspended for a repeated trangression of a rule, for an act that harms another player or for a violation that jeopardizes the integrity of the game (gambling for example).
Spitting is like pushing or shoving in terms of the impact it has on a player(s) and the game. It's one of those "lesser" offenses that will merit a fine but not a suspension.