Based on you post and posts by jesse, I'd say the issue is Costco, or the relationship between Costco and Disney, or perhaps your geographic area.
In the Cleveland / Akron area PIXAR is well represented in all the stores as far as DVD adn VHS sales and rentals go. Best Buy and Circuit City are the major retail outlets, but even the local grocery stores (i.e. Tops, Giant Eagle) have plenty of Pixar product.
Also, the local Blockbuster and Hollywood Video are well-stocked as well.