He addresses just that. Feeling bad is one reaction, feeling betrayed and entitled to limitless updates of an app that you like is something totally different.
He also makes a bunch of assumptions (of course they asked google about open sourcing, but google said no for example) and also skips over other serious problems (things sparrow said they were working on for the future).
Sorry, but this article is pretty bad.
"Sparrow OWE me new features, since when you're buying a software produced by a startup, you're also supporting the development."