Schumi's sportsmanship? Well he is just hungry for being the best. Schumacher, Hamilton, Alonso all have critics slamming their 'sportsmanship' but they have one thing in common... the desire to win. Not drivers who are fast but become a mouse when challenged ala Massa.
As much as it seem to be a 'low blow' as you call it, I think its still fair because it is a legitimate place to still compete for position. It is after all still a place for competition. Perhaps massa didnt think that ALonso will pull that stunt on him. But I guess he has only himself to blame for not being alert and defending his position.
Hamilton and Vettel? Fair and square, rival teams anyway. only the exit where i felt hamilton should have hanged back. All rights to vettel for holding his position.