Actually I looked it up. You are wrong. Via the report:
"Game Software includes physical software sales and digital software sales (including full-games and add-on content)."
"Full game software digital download ratio is calculated by the following formula: Full game software units sold via digital transactions/Full game software units sold via both physical and digital transactions"
So digital only games do calculate into their formula to figure out the ratio. The only stipulation is that it is a "full" game, which basically just means it doesn't count DLC for the ratio.