Logic Pro X does not have a downloadable demo from the store or Apple’s site. It costs $200. The previous version that was available the day before Logic Pro X also cost $200. Apple balanced its price at a perceived value for both new and existing customers. Now, over time, Apple lowered prices on some of its apps—Aperture used to be $300, now it’s $80—to maintain that balance, but it’s never done upgrade pricing or even sales.
We seem to have an uproar over the App Store's lack of upgrade pricing every few months. I understand why developers want upgrade pricing. They're used to it and it helps gather valuable information about customers' willingness to pay. But Apple has a history of prioritizing its customers over its developers, and I think that for the vast majority of its customers, a simpler pricing structure makes sense. You buy it, you own it, and if the developer wants to get more money out of you with the next version, they have to give you a reason to buy the whole thing again.
The downside is that it keeps developers from using pricing as a way to reward existing customers for their loyalty. The upside, however, is that it weakens the lock-in that prevents users from trying new apps that they might otherwise have missed. Think about the customer who keeps buying a product because he gets a discount every time he upgrades. Now eliminate that discount and suddenly he has reason to look elsewhere. The process may hurt established developers, but it provides a great opportunity for up-and-comers.
The best thing for developers to do is to stop worrying about when upgrade pricing will arrive. It won't. Instead, focus on making great apps and pricing them to their value.