There are a very large number of webomics that use traditional means for their art - however, the trend on Webtoons leans more towards digital art.
Digital methods, from a functional stand-point, are more suitable for quickly churning out material, with the application of colours being as easy as adjusting the colour wheel and a few strokes of the brush.
I imagine this would be crucial for the artists up at the top - they have deadlines to get to.
Also, the comic I work on (Project SHaDe) is largely created with traditional methods - have a look if you're curious.