Of course. If I remember correctly from that Barca documentary, Txiki and Soriano basically gave away all money prize from winning La Liga to their players back at Barca through bonuses. So the players must believe City can win PL or some other trophy in the future if they accept a lower base wage.
If Nasri really took ~£40k less in basic salary, the bonuses will be huge as you say. Let's say £5k a match, £2k a goal. Minimum five matches in a month gives £45k, two goals £4k. He will be injured and lose bonuses, but on the other hand there will be months with 8-10 matches.
If City don't win anything, City won't pay out as many trophy bonuses. With this way of thinking, the players must truly believe that City can win trophies in the future, and why wouldn't they?
It's more fair towards everyone. The fans, the club, the players. Everyone will work towards more success. When Robinho was signed for example, no way he would take trophy bonuses since he knew City wouldn't win any. Today, however, it's different and *every single* contract has been re-negotiated.