I know you mean well but their are some things to be corrected:
1) The European population goes over double the North American population.
2) Therefore their is a high (maybe higher) demand here that's also willing to pay over double price with only 15% of the price is going towards VAT. All for the same stuff.
3) I see the logic, but if you take a look comparing the releases of every game Harmonix was involved with except GH2 and GH:ERot80's, you'll see they have a nasty habit of terrible release dates unmatchable by any other developer. It seems the problem lies purely with them and at this point I find hard to believe it could still be about money anymore. Bad European release dates died with the 90's. GHWT is Neversofts first game to include drum technology but they've managed to top Rock Bands sequel, let alone RB1. On that note, I'd also be surprised if it were to be about laws.
By the way I believe hearing somewhere that the peripherals work with any game disc. It doesn't matter whether it's PAL, NTSC etc. So production of those shouldn't be any different.
I don't see what it is I could be missing if there is actually anything.