I wouldn't really bother that much, since distinguishing details tend to be a pain to remember and execute the same way over and over again throughout the course of a webcomic
I think if you're good at portraying personality, you'd probably be able to tell who is who based on dialogue/body language/behaviour alone even if the look exactly the same 
I'm not that good myself though, so I try to give main characters different hair/eye colours at least just as a shorthand for "character X". I'm not that obsessed about accurately portraying realism XD
I'd probably try to vary characters a bit more in more static media where you can recycle your drawings though, like visual novels 