The buzz around Apple’s official unveil of iOS 5 and iCloud was deafening — but Instapaper developer Marco Arment’s one-word (one expletive, actually) Tweet ^[1] from June 6th cut right through the noise.

Why the Tweet of resignation from Arment? Probably because the newly-revealed Reading List within iOS 5 provides pretty much the same “save a Web page now, read it later” functionality as Instapaper — and Apple didn’t buy out Arment to get it.

As Gizmag points out ^[2], this is the fundamental problem with developing add-ons with broad applicability to a vendor’s customer base: The fact that it’s not automatically available from the platform provider is problematic to them, and sooner rather than later they will solve that problem, with the early developers holding open the door. Arment didn’t invent offline reading, he just created the most popular app for doing it; Apple’s Reading List version of said functionality has a captive audience thanks to the popularity of the devices on which iOS 5 will run, meaning Arment — and other developers in the same situation — can’t compete.

Remember, developers: stay vertical. Selling a niche app that just one or two percent of platform users are willing to pay for can still make for a solid payday, and cuts down the likelihood the vendor will look to add the functionality into the next iteration of their OS.

Read 6 Tips for Beginning App Developers ^[3].