Thanks for considering it. While it may be fewer taps, for me hitting the ">" button breaks up the reading flow; you are taken to an entirely different screen to read the example sentences, then need to go back to the reader screen and find your place again. I generally find it difficult to find where I left off reading in a page of Chinese text. Maybe if hitting ">" then going back kept the original phrase highlighted with the pop-up open, it wouldn't break the flow as much.
Also, from a purely ergonomic standpoint, the ">" button is in the bottom left in the reader screen, but the "go back" button is in the top left of the definition screen. It's a minor point, but on a larger device like an iPad you do need to shift your hands about, and it's much less smooth than just tapping the word to open the pop up, scrolling, then tapping outside the pop up.