If you look at Sherlock in the pilot episode it is even more striking. Ok, Dylan looks quite different because he's drawn by many artists, and he's changed a bit over the years, but especially in the old covers, in which he had often wavy-ish hair, he has many things in common with Sherlock. (BTW, Dylan Dog is meant to have some things in common with Sherlock Holmes, so...yeah.)
For those who know only the Dylan Dog of the american movie, I know it can sound kinda crazy, but look at the original comic and it will make more sense, also because in the comics Dylan lives in London. (And I still don't get why the movie had to be set in the USA...) For those who have never heard of Dylan Dog, check it out if you can.
(Pics to prove my point will come later when I'm using my laptop.)