GTA: Chinatown Wars no longer a DS exclusive

I usually tend to stay away from news directly unrelated to Nintendo platforms, but I thought that this was pretty significant. Rockstar announced today that Grand Theft Auto: Chinatown Wars will be heading to the PSP later this year. This obviously means that the title is no longer a DS exclusive. I’m just wondering how the touchscreen controls will be changed for the PSP version. And also, why was this move made in the first place? Perhaps to increase sales of the title?

Source