No, Maurice is right. They're casting actors, not models, so they go for talent (supposedly) and personality more than superficial resemblance. The show was in a different reality from the movie anyway, so it didn't matter what the alternate versions of the characters looked like. (Or sounded like, since both actors had American accents instead of the English accents York and Agutter had. Which really makes more sense if they grew up in a domed city near Washington, DC.)
They cast a Farrah type as Jessica because Farrah Fawcett had become hugely famous and they wanted to capitalize on that. Even the movie's own publicity deceptively played up Fawcett as a major part of the film. It wasn't ignorance, it was a deliberate choice to ride on Fawcett's coattails (although that's a poor metaphor for someone whose fame came from a swimsuit poster).
After all, casting directors don't work in isolation. They work along with the producers (or the director of a feature film) to sort through the possibilities and pick the best actor for a role, with the producers making the final call. And the producers were obviously familiar with the film, as they incorporated its stock footage and reused its costume and prop designs. Indeed, the first version of the TV pilot was co-written by the film's producer Saul David and the novel's co-author William F. Nolan. So yes, of course the makers of the TV series knew damn well what the cast of the movie looked like.
But what does it matter if an actor looks like the movie character if they aren't good enough or reliable enough to make it as a TV series lead on a weekly basis, possibly for years? Or if they don't have the right chemistry with the other actors? There are more important considerations than appearance, and any competent casting director or producer knows that. Sometimes you get lucky with an actor who's right for the role and strongly resembles the original (e.g. Michael Shanks as James Spader's character in Stargate SG-1), but sometimes you choose someone who has the right personality but doesn't look a thing like the original (e.g. Gary Graham as James Caan's character in Alien Nation, or Don Cheadle replacing Terence Howard in the Iron Man films). The look is the least important part.
