Nightwish may just be the most organized band on the planet in terms of how far in advance they plot their schedule. I'm almost certain that they even have a rough outline of 2008 complete as well.
That leads to the problem on the touring dates announcements. Their U.S. booking agents gets the dates from the band and then starts working on a touring route very early. He contacts the clubs now with the date and info. He cannot give the clubs "tenative" information as the clubs will not book them based upon a "maybe."
As others mentioned, the clubs are a big part of the problem now as they have followed Jaxx's lead of announcing stuff they moment they hear about it regardless of whether there is "official confirmation from the band" as they deal with the booking agent, not the band. That's why they announce ticket info, etc. immediately. This is not a new practice, but you cannot expect the same results now that the internet is what it is.
Those "coming soon" signs are a situation where a booking agent contacts them to gauge potential interest for the show and get an idea of their calender, but is not ready to commit a date to the club.
Regardless of the removal of the dates from public eye, I'm certain they are legitimate. It's a matter where Nightwish is trying not to announce everything prior to the public announcement of their new vocalist.