I honestly just feel they didn't make a definitive release date because they are trying to perfect it before release and are just running final test or other such things. Doing so might bring up problems that can be quickly fixed, but might delay the release a little. I would prefer they spend a little more time as opposed to releasing it to us a little early and we play a broken mess. It seems perfectly reasonable though because they have been working on 0.4 for what seems to be years and one single month seems minuscule in the grand scheme of the progress.
However, I do hear you. It is a tad bit annoying to have a release window of a whole month and it is very true that this announcement has cause increased traffic to their website, but I'm sure that wasn't their intention. But hey, if they're trying to do that then it is of 0 concern to me because they've made a great mod for free for all these years that doesn't require us to pay.