Digital can have problems too, just not the same exact problems. Analogue gets gradually worse with longer cables. Digital will be fine up to a certain length, say 14 feet, but then 15 feet will be utter crap (just using random numbers as examples).
I don't think Displayport is as bad about it, but this has been a major problem with HDMI cables, especialy cheap ones. Being digital does not automatically mean you can make a cable as long as you want to. Ethernet is the best documented case of this.