Having to change a road map is totally different from giving a fixed date 3 weeks out from a single update. Road maps are based on predictions and as such are liable to change once work has begun on individual elements and more is known. They have been working on the heath and home update for a while now and as they've given a firm date for its release they have highly likely got it to a play tested stage where it can launch and they are using the remaining time for spit and polish and, as you have mentioned, to drum up marketing for it and get as many of the original player base back and playing again.