Marco Arment reads between the lines. He interprets well, but his best point comes at the end of the article, where he responds to the comparison of Twitter’s API rules against Apple’s App Store guidelines:
Many uses of Twitter’s platform compete with Twitter on some level. Twitter doesn’t need a lot of its nontrivial apps, and in fact, they’d be happier if most of them disappeared. Twitter’s rules continue to tighten to permit developers to add value to Twitter (mostly “Share on Twitter” features) but not get nearly as much out of it (e.g. piggyback on the social graph, display timelines, analyze aggregate data).
By comparison, Apple needs its apps much more than Twitter does, and Apple’s interests conflict much less with its developers’. Even its famous anticompetitive rules, such as the prohibition against “duplicating existing functionality”, have been minimally enforced and have actually diminished over time.
Apple has another big advantage over Twitter: the latter is very transitory, and therefore replaceable. Yes, we will all bemoan the crapping out of a used-to-be-good service, but we’ll get over it. But if Apple were to shut down the App Store tomorrow (or were to severely restrict the abilities of developers), we’d see a huge backlash (remember section 3.3.1?). Apple needs their developers. Twitter would have an easier time if they lose their developers and control the entire stack.