Doug,
Your problem is that you are thinking in English to understand.
In Spanish you could perfectly ask: "¿Estás viniendo a casa en estos momentos?" because you want to know exactly how many minutes do you have before he/she arrives. But anyway, in a regular situation you would ask : Vienes a casa hoy?, mañana? etc
That means that the present continous in Spanish has a similar usage than in English but NOT EXACTLY THE SAME. If you want to get used to it, just listen, read, talk with natives etc.