Hey there! 
First off, I’ll have to admit that I don’t know all the ins and outs of shipping. (I mean; I dó know my shipping, but that’s something completely different.) However; I can give you my best guess. Which would be: for jimmyjoy-plennyshake, it’s just too hard to determine many radii from jimmyjoy-plennyshake HQ, with each radius having different shipping costs. Instead, I think they just categorised all the countries, took the average shipping costs for each and every group, and set that price as the shipping costs for the whole group. I’m just guessing that jimmyjoy-plennyshake makes a bit of profit on orders below 25 euros in Amsterdam, The Netherlands, and loses some money on orders that are very heavy and have to ship all the way to the southern-most part of Belgium. My point is; for the sake of simplicity, it doesn’t matter where in France you live; the shipping costs for all of France are the same.
Which brings us to your fair point: Sweden and The UK are farther away from Amsterdam than most of France. Again, I’m no expert, but I can imagine that there’s quite some variables involved. Some ‘countries’ might order quite a lot of jimmyjoy-plennyshake. It might be cheaper and easier for jimmyjoy-plennyshake to just send a big batch all the way to Sweden every now and then, and then send the orders from Sweden from there; lowering the shipping costs for its inhabitants. They might want to promote their product in some countries more than in others, for some business-y reasons (and lowering the shipping costs in those countries might help them with that). Or, shipping to some countries might just be cheaper than shipping to others (they use different services all around the world, every one of them having different rates).
Of course you might want to wait for an official response, but I was bored and it was kind of fun for me to ponder on your question (good question!) Maybe commenting in the retail thread will help you get jimmyjoy-plennyshake in stores in France quicker, saving you all the shipping costs.
Anyway, those were my three bits. G’night!
(P.s; TwiDash == best ship)