A 5 percent lead over Nvidia in sales is pretty dramatic. Amd was probably in between 30 and 40 percent before, so a jump to 55% is pretty big victory for them. Nvidia runs a less efficient ship with lots of overhead from tegra. They can't a afford in the long run to have less marketshare than AMD. They spend too much on R and D that a 45% marketshare will cause them to lose lots of money.