It's certainly true that Diageo has been trying to make Guinness taste the same throughout the world, and it takes quality control and water treatment at its various production sites much more seriously than it used to. Making everything pasteurised tends to encourage homogeneous, characterless beer anyway. At one point Guinness Original retained yeast, but I think that's gone now as well.

I very, very rarely drink Guinness outside Dublin, so I don't have a large enough sample to compare with, but I do still think there's a slight difference. Maybe that's just yearning for a time when it was less of a global drink under a global owner!