Yes, I have seen this port in my Alto too. The last time i complained about my power steering losing power and working as Manual at time and a "thud" sound while driving on potholes, Maruti service center has connected some device through this port which looks like a fat tennis racket to check the complete system/car details. They have charged 300/- for using that device. Finally it indicated towards the fuse box as faulty and the fuse was changed to solve the issue for good.
I guess all models have it from Omini to Latest in Maruti to my old bolero(2007).(not sure of other cars).