Reversing a previous ministry's decision simply because not doing so proves awkward or even embarrassing is a pretty poor precendent.
The Forfeiture Committee decided that:
Both the Financial Services Authority and the Treasury Select Committee have investigated the reasons for this failure and its consequences. They are clear that the failure of RBS played an important role in the financial crisis of 2008-9 which, together with other macroeconomic factors, triggered the worst recession in the UK since the Second World War and imposed significant direct costs on British taxpayers and businesses. Fred Goodwin was the dominant decision maker at RBS at the time.
In reaching this decision, it was recognised that widespread concern about Fred Goodwin’s decisions meant that the retention of a Knighthood for “services to banking” could not be sustained.'
As Alex says, that's probably more of an argument for not giving knighthoods to bankers until they retire (or become chairmen). Rough justice then, and perilously close to mob justice. RBS was by no means the only recklessly managed bank, nor was Fred Goodwin the only executive at RBS.
But then I suppose that's rather the point. A Chief Executive, like a destroyer captain, is responsible whether or not he's to blame. Fred Goodwin was richly rewarded both financially and with what might be termed the trappings of office for his apparent success. His knighthood was awarded for his contribution to the banking sector; it's not obviously unfair that it should be taken away for precisely the same reason.