They are being conservative, but more like they are being realistic. Iwata can't throw out a bullsh*t forecast this year because his leadership position is up for a vote of confidence from the shareholders in June.
If he made an overly optimistic projection again and say Mario Kart doesn't give a big boost, it could fuel anger from investors who on the fence on Iwata if he looked so wildly out of touch again.
I almost suspect Nintendo may have been able to release Mario Kart a month or so earlier but opted for a late May launch so the shareholder meeting in June could not be swayed by a post-Mario Kart Wii U lull that would damage Iwata's chances with shareholders voting on him.
If they launched in April or early May, investors would be able to see if Wii U sales dip back down after the initial few weeks of sales.
