The CEO of Avatron Software explains his rationale of having a Professional version of Air Sharing as below.
We love our early adopters, whether they got Air Sharing for free, as over 80% did, or bought it. You guys are awesome! And your suggestions and enhancement requests are extremely valuable, which is why we have this suggestions forum.
Soon after releasing Air Sharing, we planned to have two versions: Air Sharing and Air Sharing Pro. Air Sharing would feature a file server and a file viewer. Pro would add Printing, Emailing, access to remote file servers, a custom PDF viewer, zip & unzip, and a host of other features. And we planned to price them at $5 and $10.
But we also wanted to offer a $5 paid upgrade for Air Sharing users. Unfortunately, Apple has not yet added a mechanism for paid upgrades to the App Store. So we decided to simulate such a mechanism, by offering Air Sharing Pro for only $5 for a brief period. It’s something of a blunt instrument, this method, because we have to offer everybody the $5 price, not just current Air Sharing users. But that’s okay. If a universal discount is what it takes to reward our customers, that’s what we’re doing!
So in effect, if you bought Air Sharing for $5, you can get Air Sharing Pro for $10, which is its regular price. If you got the classic version for free, you get Pro for $5, a Right Bargain. If you bought Air Sharing for $7, you’ll have paid a total of $12 for Pro.
I hope this clarifies things. One other point: we also fixed some bugs in Air Sharing Pro that we do plan to fix in Air Sharing.
For example, we made enhancements to the UI, made the PDF viewer much more stable, added support for viewing iWork ’09 documents (as long as they’re saved With Preview).
Our intent is NOT to make people pay for bug fixes. We absolutely plan to roll those bug fixes back into the classic version of Air Sharing as soon as possible. This would already have happened had we not gotten ensnared by the sudden requirement to support iPhone OS 3.0 before Apple will approve apps. But it will happen soon.