i still think that most times its been on the 15th. except in cases like last time this was brought up, that a sale was ending that day and they most likely didn't want to have the new preorders for sale too.I guess "end of the week" (or "start of the week") trumps "15th of the month" when it comes to announcements.
another occasion is when they are trying to get a bigger than usual amount of releases together and aren't quite ready to announce since they are still determining what they can release in that 3 month time period and what needs to be pushed to the next month.
that being said i think tomorrow we'll see a pretty good size amount of releases (especially considering last months meager amount/relatively humdrum releases).
my guess is def. wings of desire (overdue) and cronos for sure.
plus maybe a surprise or two....
please note this is pure speculation (and a little bit of hope