Flash memory is a massive growth market which is progressing very quickly, evidenced by the fact that memory sticks and cards that are orders of magnitude larger in capacity than those a few years ago are many times less expensive.
This is good for the consumer in that it has driven down prices, but at the same time, with the sheer number of products and variations available, is it really realistic to expect a local shop to stock all sizes of these products? If you can get a 2GB card for a tenner, then the price they'd have to sell a 512mb or 1GB version wouldn't be worth their time stocking. It's not about being awkward, it's about financial viability for a walk-in shop with overheads to consider.