Features unique to the Android version include: automatic Google account integration, third party keyboard support (Swiftkey for example), deeper integration with the phone book. and Stacked Notifications (multiple notifications automatically stack so notification screen doesn’t get cluttered).
In an interview with TabTimes last month, Quip cofounder Bret Taylor said collaboration features are key to the company's strategy:
“Collaboration is not integral in a lot of products," said Taylor, former CTO of Facebook. "We found that people use documents less and that the main purpose was for sending them to others. Collaboration really resonates with business and it’s our central feature."