Keep in mind that when apple started to really outdo microsoft in the marketplace, I started to see a coordinated attempt to place negative stories about Apple in the press. I think the "iPad is just a big iPod touch" meme was one of those stories that took off. When you have nothing to compete against the iPad, you place ideas in the market designed to reduce demand for the iPad.
For what it's worth, I've yet to hear an iPad owner think it's nothing more than a big iPod touch. We know better. As I said here a month ago (and then later saw it being used in the tech media), the iPad is like an iPhone the way a swimming pool is like a bathtub. They both hold water so that you can immerse your body, but there are many things that you can do in a pool that you just can't do in a tub.
Couldn't have said that better! And you are probably right, but it's unfortunate it caught on, all my friends except for me are convinced its useless.