It is surely beyond question, whatever spontaneous commentators said at the time, that to make a white ball - especially a new one - swing at night in South Africa is not the hardest task.
Both have struggled to swing the ball at times in different circumstances, and both have struggled with control on plenty of occasions.
The fact is, both bowlers took advantage of the conditions but, like the New Zealand-India Tests, the conditions helped the bowlers so much that the achievements must be taken in context. And that context is that you are unlikely to find better conditions for swing than at night in England\South Africa\New Zealand, and you are unlikely to find better conditions for seam than those pitches for the New Zealand-India Tests in 2002\03. It is similar to achievements against Bangladesh being taken in the context that most of Bangladesh's batsmen are nowhere near Test-class and hence they play poor strokes with regularity.
And as for Nehra cleaning-up the Sri Lanka tail, no, it's not his fault that he didn't get the chance to bowl at the top-order, but nor are the poor shots the tail did play to his credit. And given that he gained, not lost, it is credit, not fault, that matters.
But I do agree that he had 3 other good performances in WC2003 - in one-day-cricket, you don't have to take wickets to have good figures.