First of all I'd like to point out that O'Driscoll was SHITE!
and secondly, that Tonga'uiha was cheating during scrum time,
if you want video evidence, watch the match... 2 examples, not arsed doing more.
Scrum for first try at 6 minutes: Tonga'uiha pops up and use's his binding arm to push Ross up and into the scrum.
Scrum at 19 minute: Tonga'uiha drops his shoulder, pushes Ross up, then use's his binding arm to pull Ross's leg(so he was unable to get balance) and drove him back.
I also noticed him rapidly dropping the shoulder on the sly as soon as they engaged, on quite a few occasions.
Also, A team doesn't just get "tired" after a 10 minute break. Leinster have played as many games as Northampton have, and you'd also have to take into account that half of their squad we're involved with Ireland, and also in the 'British and Irish Cup'...
In terms of money, although they do have more. Leinster spend as much as the English clubs do, and their only aloud to have 4 foreign Internationals on the roster!