Good question, for which I don't know the answer. The nice thing about this calculator is that it is based on what real photographers have actually been paid.
But you also need to keep in mind that these are prices based on stock agency fees - so there is a mark up to cover agency fees and overheads. If dealing directly, (ie - you have no overheads or agency fees) perhaps you should adjust your fee accordingly ... maybe by as much as 30%.
Speaking personally, I have never used a separate charging scale for US and Europe, but I do have many more US sales ... perhaps thats why
And of course, regardless of this calculator, remember that many magazines simply pay a fixed rate which is non-negotiable.
Colin K. Work, Pixstel