No comics don't have to be digital. Some creators prefer digital, some prefer traditional and some like to use a little bit of both like traditional inking and digital coloring.
I'm one of those people that like adding a little bit of both 
Stray Dog by VanRah is traditionally inked and digitally colored
Sacred by Lizbeth R. Jimenez is all traditional along with the coloring.
The only digital she uses is for the sound effects and the text.