Could present some advantages.
The original iPad came in right at the end of the iPhone OS 3.x era, and the iPad 2 was released with iOS 4.3, with iOS 4.x already being quite mature. Shifting the iPad later in the year would align it to the start of an OS cycle; this may or may not be a factor for some parties.
Also, it baffles me that the iPad comes out with the same proc as the forthcoming iPhone but half the RAM. Wtf? Is this down to component cost? A shift to later in the year may help with this, but that's a fairly outside statement to make so I put the disclaimer here.
On the other hand, putting the iPad release alongside the iPhone releases causes congestion at the end of the year (along with iPods, in whatever form they take in the future) with virtually nothing in the Spring save possible Mac hardware updates. I can see the logic in the iPhone and iPod Touch releases being aligned since there isn't much difference between them and the iPhone had been taking up too much time at the WWDC keynote for too long, but the addition of the iPad doesn't make business sense when it's selling so well; the ideal situation would be to balance revenue across the year as far as you can control (excluding the obvious upturn in sales at Christmas).
Ah well. Another day, another iPad/iPhone rumour.