In theory, there's nothing particularly wrong or uncommon with this approach. I mean, if you buy Windows 7 Home, and want to upgrade it to the Ultimate version, you just enter a new license key and off you go. It's the "same" OS, just with some features disabled in the Home version.
Of course, with hardware it's a little different. A CPU being deliberately sold with some of its hardware disabled (or crippled in other ways, such as reducing the multiplier) is going to be more expensive than a cut-down model that simply doesn't have that hardware. Although some of that might be offset by lower production costs, since there is still a fairly high overhead in setting up manufacturing for a cut-down design.
While it might make financial sense in some situations for the manufacturer, it usually doesn't come across well to customers. It doesn't take a genius to see that they're still turning a (smaller) profit at the 'crippled' pricepoint, so the price difference between the crippled and uncrippled version of the software/hardware must be pure profit. At least with software, you can argue that there are higher support costs for a product with more features, so there is actually some extra cost they have to shoulder as well. But with hardware, it's just them trying to make more money.