Those statements apply to any OS, not just iOS. Other operating systems have chosen to support the configuration of default apps, despite the extra work and the extra limitations inherent in that type of design.

Without that feature, looking at it from the outside, it makes iOS look like it's still not a mature operating system. Either that or it makes Apple look like they're trying to push their default apps on us and to downplay third party applications.

Funny thing is, despite all those arguments against having default apps configurable in iOS, now that I think about it, I've seen evidence that there is already low-level support for this in iOS, and it's been there for while. For instance, the third-party YouTube app gets launched when I click on a YouTube link in some other third-party application. That's exactly the sort of behavior I'm talking about, the only missing piece is the dialog box where I get to configure which app plays Youtube videos.