Well they got slapped for including IE forcible by the EU and there was never an App Store like that over XPs lifetime to my knowledge?
Also you could quite easily replace the whole Shell. Sadly not anymore if you do that now stuff you need access to will just stop working because everything "metro" will need the explorer shell actively running in the background.
Windows Catalog (which I totally don't rememeber at all... was it in all the builds or only some regions??) was apparently "the showcase for products that are designed to make optimum use of Windows XP. Go digital, and discover a great new computing experience!" [1][2] More of a catalog listing software and hardware that got the designed for XP logo, rather than a place to buy those things, let alone an app store experience. At that time, it was much more common to purchase applications inside an actual store.
