Apple’s App Store has quite a storied history when it comes to which apps get rejected and which get accepted. For the first few years of the App Store’s existence, there often appeared to be no apparent rhyme or reason to which apps were allowed and which weren’t. Things got a bit better when Apple finally got around to publishing guidelines that were publicly available to developers in September of 2010, but some problems remain. Even with the guidelines in place the app review and approval process can seem a bit arbitrary at times.

That’s the way it probably seems to the developers of several apps with Dropbox integration. It seems that since the release of Dropbox’s latest software development kit (SDK), the App Store’s reviewers have been hitting apps that use Dropbox with a ban-hammer as fast as devs can submit them. The problem first came to light over the weekend when developers started posting to a thread on Dropbox’s developer forums, saying that Apple was rejecting apps that used the new SDK. Multiple devs chimed in, saying that Apple was issuing rejection notices for both new apps and updates to old apps.

So, why is Apple rejecting these apps? Are they somehow using Dropbox’s SDK to bring porn into the App Store (something Apple has always rejected)? Are they using it for some sort of scam? Nope. It turns out that the new Dropbox SDK is guilty of the grievous sin of sending users who don’t have Dropbox installed on their phones to a page on Dropbox’s website that includes a link they can click to pay for more storage space. That’s it.

You see, there’s a section in Apple’s app submission guidelines that prohibits apps from providing “access to external mechanisms for purchases or subscriptions to be used in the app.” You see, Apple wants all purchases made for apps in the App Store to go through Apple, so they can have their 30% cut of the sales price. You may recall that Amazon and Barnes & Noble ran afoul of this particular rule last year. Their Kindle and NOOK apps provided links that sent the user to each company’s e-book store in Safari. That way users could purchase Kindle and NOOK books from their iPhone or iPad without requiring Amazon or Barnes & Noble to fork over 30% of the price of every book purchased.

According to Apple’s reviewers, Dropbox’s new SDK violates this rule. As with many services – e.g., Twitter, Facebook, etc. – when you download an app with Dropbox integration, you have to authorize it to access your Dropbox account. Of course, not everyone who downloads such an app has a Dropbox account, and not everyone who has a Dropbox account has the Dropbox app on their phones. For those people, the SDK now directs users to Dropbox’s website in Safari, where they can either authorize the app to use their Dropbox account, or create an account if they don’t have one. On Dropbox’s account creation page, there’s a conveniently located link that you can click to pay for more than the 2GB of storage you get with a free Dropbox account. That link, it seems, counts as an “external mechanism for purchases or subscriptions.”

In response to the problem, Dropbox posted an updated SDK that removed the link to the desktop version of the Dropbox site. The updated SDK, though, is intended to be a temporary workaround while a better solution can be found. In a statement to The Verge, Dropbox representatives said that “Apple is rejecting apps that use the Dropbox SDK because we allow users to create accounts,” and that Dropbox is “working with Apple to come up with a solution that still provides an elegant user experience.”

It’s not clear whether apps using the upgraded SDK are starting to get into the App Store yet, nor what kind of solution Apple will find acceptable.

What do you think? Is Apple’s rule reasonable, or is it ridiculous? Let us know in the comments.