I believe that's not quite correct. Emirates were the first major operator to go for 10-across 777s instead of 9-across, but had done it along with extending the legroom to I believe 35", on the basis that the square area was the same but it was better to have extra length than width.
BA and others coming along on their coat tails have changed their 777 seating to 10-across as well, but without the extra legroom.
I also wonder what impact it will have on the front row. These seats on a BA 777 have always been narrower and felt more squashed, because the tray table comes out on a pantograph arrangement from in the armrest instead of dropping down from the seat in front. The actual seat cushion may be the same width but you are constrained by the thicker armrest, which are also non-raiseable.