Wow, this is pretty bad reporting. iOS did not represent the vast majority of U.S. "online shopping." The stats are related to MOBILE shopping.
Are you sure about this? iPhone is about 42% of the smart phone market in the US, but iOS also includes iPod Touch and iPad. When those are included, I would guess that iOS has a higher market share than Android.
The report does include tablets too. where it compares phone sales to tablet sales.