Interesting, at first pass I’d say the source availability has little to do with the topic at hand. But on second thought it might be rather significant. No company would finance making 2x identical cross platform apps, but if you have a pool of OS folks who are free to contribute at their leisure, the calculus changes a bit.
But isn't the whole point of linked article is that author doesn't like regular apps because it lacks control over UI and functionality compared to Web apps?
Being open-source is kinda even better in that regard.
But tdesktop is really well-made Qt piece of software, snappy, feature-rich and multi-platform.