I will just say what I said about it in the Vita thread:
"The only way I can justify it is that it's actually quite a sensible prediction. Last year, even with Call of Duty/Assassin's Creed, it sold 3.5 million for the year. If it sells that again with a bit of a boost + 1.5m for PSP then it'll be bang on their prediction. Perhaps they're just being sensible; and that there is software coming, but it won't provide that big of a boost."