Very, very smart. There are many who will buy the most storage capacity available, even if they never use all of it. Apple must have done their analysis to figure out the demand for this.
Could also be the first step towards rationalizing the product line. Retina mini iPad with 16GB, 32GB, and 64GB. Retina big iPad with 32GB, 64GB, and 128GB. Or, something like that. Kind of like the Macbook Pro line.