Presumably Rebellion are trying to make a splash in the US, as a) Crusade has never been reprinted before and b) They can plaster Grant Morrison and Mark Millar's names on the cover.
However, as you say, Crusade is such a weak story it's likely to put off more readers than it attracts. DC tried this approach when they pushed Judgement Day in the US on the strength of Garth Ennis' name, and that sank like a stone.
To make matters worse, they've also commissioned Brian Bolland to draw the cover! What a waste...
Imo they'd be much better off publishing a new edition of the America tpb. Granted Wagner isn't a name in the states, but the material is way stronger and would make a far better impression of Dredd - might even challenge a few preconceptions of what the series is about, too.
I'm especially worried because by my calculations Crusade is due to appear in Case Files vol. 23 anyway, around 2013/2014, so does this mean that series is going to be discontinued?
Doubt it - after all there's been a fair bit of overlap already, what with the PJ Maybe and Mechanismo stories already being published in both the Case Files and the standalone trades.