Back to the original topic,
Much of what needed to be said about the reasoning for the publishing of a 2nd edition has already been said. I'm speaking as a grognard, but confessing that the v1 rules had their limitations. V2 brought some fixes, and as others have mentioned, these fixes were imperfect.
In regard to the setting, I honestly think that BI deserves thanks from the grognard camp for not ditching the old in favor of the new version of the WH-world, but for trying their best to show how you could read the v1 WH-world into the GW-mandated world. Knights of the Grail, I think, is the best example of that.