It's a native app built in XCode. Except for the navigation bar background and icons, it's all drawn manually in the app. I found it to result in a much faster experience.
One change I didn't mention in the post is that I finally moved from ASIHTTP to AFNetworking for my networking library. That's significantly faster as well
The premise of my post is that your first assertion ("an icon is an ad") is not a fact, but a choice. If you search for "email" in the App Store, would Sparrow jump out at you? No, but they've chosen not to pursue that "advertising" strategy. Their growth is based on fully delighting their users with the product, and an icon which, IMO, looks like it always belonged on my phone.
Sparrow's growth comes from happy customers (and some traditional advertising), not an icon that looks like an ad.
I'm curious how you A/B test app icons...Do you switch from one version to the next and compare downloads?
Also, can you clarify what you mean by "developers are...incentivized against #2"?
Haven't used them, but it might be worth a shot