One of the things that the article didn't mention that I think is worth bringing up is how we eventually plan expose parts of a "payroll API" which can make managing payroll much easier. For example, I would imagine that tabbing through text boxes to enter hours for 120 employees every 2 weeks can get pretty tedious and error-prone. Well, we actually have a (currently internal) API for that, which can eventually be integrated into, say, time tracking software. We believe similar benefits can be realized by integrating our API with accounting software, expense reporting software, etc.
In fact, we've architected our system to be an API from the start, and our JS web-app is just a consumer of our API.
I'd love to hear some other ideas people might have that could take advantage of a payroll API!