In a recent post, John Gruber speculates that the iPad will get another revision to bring it's release schedule in line with the iPod. Read the full post here: Daring Fireball: The Next Six Months. John is great at analyzing Apple's product cycles and update strategies to accurately predict what's coming soon from the company. Combined with a growing group of sources close to or within the company, and he should (and does) get a lot of respect for his predictions. That said, here's why he's wrong...
He's missing a key ingredient in the mix, and that's who the primary purchaser for the product is and what the major buying events are for that part of the year. In late-sping/early summer you have two major consumer purchase events - Mother's Day in April, and Father's Day/Graduation in June (Dad's & Grads). This exactly the audience that is looking to give/get the iPad. It's a premium product with a higher price point, which I think makes it a more adult oriented product. Counter that with the fall iPod event, which is more geared toward high school/college kids heading back to school. It's also the lead up to the holiday season, and is often combined with a 'Back to School' computer purchase deal.
These two separate and focused cycles make a lot more sense to me than trying to roll them up into one. So that's why I think we'll see the iPad stick to the March/April release window. Mom and Dad get iPads on their designated days and can use them to check in on work from the backyard over the summer, while the kids get iPods for going back to school and into holiday season.