I'm really glad Gnome is embracing the idea of extensions. That said, I think trying to isolate them to some web site will be an exercise in futility.
> We want to be judged on the experience we designed, for good or bad
Remember when Gnome was still shipping Spatial long after all the distros had turned it off? I was really glad the distros could bring their desktops back to reality when the Gnome project decided to get a little too experimental. A second opinion is often a good thing.
> So why should users have to wait for someone to wrap up an extension in an RPM or DEB in order to use it?
Because it does an awesome job of weeding out the cruft. You get another pair of eyes, a lively bug tracker, and lots of fellow users all using the same system. Distros tend to be pretty fantastic. Personally, I wouldn't toss their benefits away quite so lightly.
Also, your writing implies that the extensions will have consistent high quality and be continuously maintained... That seems hard to believe. Gnome's past experience with theming sites suggests that the site will contain lots of duplication and half-finished cruft and the distros will cherry-pick the great bits.
> Why should an important bug fix be blocked on the same process?
Most security turnarounds are measured in hours or days. Not a problem.
Wait, you're going to push updates straight to the user??? Or maybe you'll send an email every time something is updated so users will have to click on install links a few times a week? Either way, it doesn't sound very desirable.
> Why shouldn't you be able to see the comments and reviews that all users have on an extension?
Very true! And the Ubuntu Software Center would be one logical place to find those comments and reviews.