The story and screen shots are based on reports from users of the Office 15 Technical Preview. No doubt, Microsoft heard from users that they didn't want to be forced into using a touch interface, and the layout of the screens shown by Foley indicates that Touch is a distinct mode of the program, allowing users to move between it and a conventional keyboard/mouse UI. Foley's source says the button doesn't actually do anything yet.
InformationWeek Tech Digest, Nov. 10, 2014Just 30% of respondents to our new survey say their companies are very or extremely effective at identifying critical data and analyzing it to make decisions, down from 42% in 2013. What gives?