It is a good and profitable idea, other things drive when things occur however. Eventually they will make one model, whether thats this year when the delta is $30 or so, or next year when its $20 or so is the only real question. Cutting down the SKUs helps hugely across the board the number of SKUs is a big problem with backorders, stock and repairs and also costs them sales. Go to a walmart or a target or an Apple store noone has all 40 SKUs for the iPad. It wasnt cheaper on a phone by phone basis to make the iPhone be one phone for all networks. HOWEVER once you factor in not having to make 3x as many kinds of phones, being able to ship a single phone to all the vendors is a huge savings. Thats why Apple did it for the iPhone and why they will eventually do it for the iPad.
Cutting down on SKUs has benefits in manufacturing and inventory management, but eventually you come smack up against consumer resistance to one-size-fits-all. If people have to make too many compromises, if they have to pay for too many features they don't want/need, or can't get the features they do want, they walk. Henry Ford's famous, "Any color you want, as long as it's black," didn't work in the long run. The competition was happy to turn that against him. And on the flip side, GM and Ford both had to shut down entire brands after going to extremes in the other direction.
The best any company can manage is the right balance between SKUs and consumer choice. In the case of 40 iPad SKUs? It's not likely that any one brick-and-mortar retailer would stock all 40. They're going to carry the models that move the best with their particular clientele. They'll bend heaven and earth to stay in stock on the most popular SKUs, but rarely worry if they go out of stock on or have to special order a one-in-a-hundred item.
Manufacturing and repair efficiencies? If they have one production line dedicated to one model, and ten to another, so long as all lines are utilized to nearly 100% capacity, that aspect of costs is a constant. And in parts procurement, the suppliers also hit a point where cost of production no longer drops with greater quantity. At that point, it comes down to how much the supplier gives up in profit margin, rather than passing along the economies of scale.