As myurr, pup and many others have said above, there is no questions about the ruling. People who continue to argue along the lines of Bob forced him off the track etc are on a hiding to nothing.
Alonso only made the pass stick by going completely off the track. End of story. All other details are irrelevant in this specific punishment. If Kubica had done something like break-test, weave wildly etc then, sure, there might be another issue to look at, but Alonso's actions still entailed intervention.
Charlie Whiting has come out and said "We told Ferrari three times that in my opinion they should give the position back to Kubica...". I very much doubt in years gone by teams would have been given such a flashing neon lights heads-up before the steward process began.
Frankly it boggles me that Ferrari were so stupid.