Well, I agree with you on Firefox. However, I can't agree where any of the other categories covered in this article are concerned. I just don't think any of the other chat clients are as unobtrusive and feature-rich as iChat (ex: my mother uses iChat to videoconf with my kids. No OSS client could do that, imho). While I agree that some OSS apps have (in the grand scheme of things) really minor features that I'd like, there just isn't anything out there that compares to iTunes/ITMS, iPhoto, iMovie, Garageband, and iDVD. Maybe the most compelling measure of these apps is that - even with the tiny amount of free time I have - I've used all of these apps for multiple projects (usually a birthday or christmas gift of some kind).
As for tabbed chats: I use Chax (http://www.macupdate.com/info.php/id/20056). So should Apple incorporate these into iChat thereby "stealing" the idea and "crushing another small developer" as they were accused of doing with widgets?