Headphones use the same method for simulating surround. However, it can't be applied to any random speakers, because as I said, you need to know the geometry to apply it and with freely placeable speakers that isn't possible.
Yes, adding more speakers helps. But they need to be placed accordingly. Either behind the listener (which isn't possible in anything portable), or as far as possible apart horizontally. In theory, vertical spacing would also help, but the current standards (such as Dolby 7.1) all take into account only horizontal coordinates. There is no surround standard that I know of that makes use of speakers placed above/below each other.
It could also help to better fill a large room with sound. However, these speakers will still sound terrible if you listen from a distance, that I can tell you for sure. So it's not that important. The current setup, however, helps you get more volume when you're sitting right in front of the tablet, which is, IMO, way more important.