Gruber seems a little more open to the idea than Rene—at least that's what I took away from his conversation on The Talk Show. But both of them definitely realize there would be downsides for Apple. I think Rene summed it up quite nicely in this paragraph…
Unfortunately, I don't think Apple would do this. It wouldn't really change the type of apps that are available -- for example, the system-level hacks of jailbreak -- and it would almost certainly lead to developers cutting Apple out of the 30% share of app sales Apple takes to maintain the App Store. Apple has shown they're not fond of end runs around the App Store for subscriptions, and they'd likely be even less so for paid apps.While I believe this is reason enough for Apple to say no, I don't believe either is a true deal breaker. Yes, Apple makes a little bit of money from their 30% cut, but they are also providing a service for that fee. They host your app, provide a way for hundreds of millions of people to find it, and make it dead simple for people to buy it. They also subsidize the hosting of all the free iOS apps with that income. If developers really wanted to take all of that responsibility on themselves, I don't think Apple would mind. I also think the Gatekeeper system being developed for Mountain Lion would be a brilliant way to enable the side-loading of apps on iOS. So why exactly do I find it so hard to believe that Apple will open up the flood gates? One word …Amazon.
If Apple were to allow apps to be loaded from other sources, nothing would prevent Amazon from creating a rival store—one that provides many of the same benefits, and is even more developer-friendly. Imagine the delight if developers had practically no fear of their apps being rejected, no week-long update waiting periods, and only had to give up 20% of their earnings to be listed in the world's largest online retailer. Unless you give your app away, I think you'd be hard-pressed to find a good reason NOT to dump the App Store, or at the very least support both. I can't imagine Apple EVER letting this happen unless some legal action forces it upon them. They will not let another company jump in and undermine their ecosystem, especially one as cut-throat and beloved as Amazon. The only sure way to keep this from happening is to remain the sole app provider, and that's exactly what I expect them to do.
Amazon already jumped in and created a store for Android apps. Imagine the motivation they would have to create a store for apps that people are actually willing to pay for.