Yes, this must be unique to the much smaller UK market, because there is barely any Potter merchandise to speak of here any more in stores. In truth, we haven't had much of it anyway. Sure, you can get a calendar or a school folder or stuff like that, but there were barely ever any toys to begin with.
Again...that's just the most daffy thing I have ever heard. And you are moving the goal post, but regardless - the most unique "in-universe" stuff is $50+ wands and $80 robes and....what else?
In any case, when it comes to scope, general merchandising of Potter is so limited comparatively - Star Wars has exponentially more characters, time periods, critters, and "factions" - I just can't see where you are coming from on this. Even just in terms of things like T-shirts, mugs, and more traditional souvenirs - you can only put Harry, the few other main characters that the general public can name, and Gryffindor on so many things LOL. Just take a look at Amazon. Type in "harry potter t-shirt" - you get about 3500 results and after a couple of pages they are all pretty much the same and much of it is just various of the school groups logos over and over. Type in Star Wars, you will get over 17,000 results.
The two just are not comparable, and at this point it is hard to say "well Potter is newer" since we are going on two decades of it being a thing.