I know! It's horrible. I just get way too perfectionist about it. I already have over 500 Pokemon, and I managed to avoid Pokemon Black and White but noo, now I have to get Black and White, and X and Y. I have a pretty darn good feeling the third in it is going to be Pokemon Z. Daaamn.
Vulpix/Ninetales is based on a fox. Flareron... well that's a good question I never really got to know on which animal Eevee and co were based on. Dogs I guess, but which kind ? Fennekin is based on... well a fennec ¬.¬;
So they look alike since they're all basically canines, plus being fire-type.