Your opinion is based on nothing whatsoever. My opinion is based on existing patterns. The iPod Touch is nothing more than a small-screened iPad, and its base model is 8GB. Apple clearly has no problem putting only 8GB in a current generation iOS device. iPhones are also the same basic device, and when Apple kept the last generation for sale alongside the current generation, they dropped the capacity to 8GB.
Now I admit that I am not necessarily any more correct than you, but at least my guess is the result of pattern recognition and carrying the sequence out to the next logical step.
I agree that 8GB is really limiting. The 8GB iPod Touch feels like a joke, and the 8GB iPhone 3GS isn't really for anyone that wants to use their phone as a full-featured smartphone. But both exist and are bought.
If Apple keeps the iPad 2 for sale alongside the iPad 3, it will be for one purpose only: lower price point. It will target the price conscious buyer very specifcally, and that buyer may not even comprehend what the real impact of 8GB means. They certainly won't care, and they might not even be buying the device for themselves. There is no reason at all for Apple not to put 8GB in it and keep their profit margin a wee bit higher since it won't impact the sales in the market it'll be aimed at.