You could argue that refusing to overturn the conviction (as the British government did a year or two back, for much the reasons you name), but issuing a pardon for the person most famously hurt by this policy, is the best middle way between letting the law of the time stand and still publicly acknowledging the wrongness of it (as was also done earlier by Gordon Brown when he publicly apologized on behalf of the government). Issuing a blanket pardon on the other hand would be just silly. The argument of how you shouldn't single out celebrities for special treatment, and what a wrong message that sends to people, also holds water, but it would only really be crucial if the pardon actually had real legal consequences for the people involved. This being a symbolic gesture, I see no real problem in letting the one symbolic pardon stand for all the rest.

I don't think it's fair to list India in the same breath with Uganda there...