Quite a lot of the current economic woes can, and indeed have, been blamed on Brexit at some point or another. At present the uncertainty of it is more damaging than the reality, but I think that's really a discussion for another time
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The question I don't see anyone else asking though is "What happens if the £ and the € recover?". If 6-12 months down the line they're both much stronger than USD, would Blizzard re-asses their prices then too? I'd hazzard a guess at no, but they could yet surprise me. I do feel confident in saying that if they both continue to be devalued then Blizzard would have no issues in raising their prices again to match.