I think including an ND variant is important for works which are polemic rather than purely informational. For example, if some person or group writes a political manifesto, they may want it distributed as widely as possible, and thus allow redistribution and commercial use. They will probably also want their name associated with that manifesto. What they do not want is someone else to take that manifesto, change the text slightly so that it advocates distasteful or diametrically opposed ideas, and then redistribute the modified version while preserving the original authors' names in the credits. This makes it seem as though the original authors are promoting the ideas contained in the modified manifesto, particularly if the modifier has (deliberately or otherwise) credited them conspicuously. The modifier need not even have bad intentions in doing so; perhaps his intent was not to embarrass the original authors but simply to reuse what he thought was very good prose and very good arguments.
Of course, this is a potential problem even with non-polemic texts; I could find some CC-licensed software manual or Wikipedia article written by some famous figure, incorporate parts of it into a distasteful manifesto, and then release it with the innocent authors' names attached to it. But I think such scenarios are less likely to occur simply because it's more difficult to attach opinions and calls to action to a purely informational text than to one which is already polemic.