Continuity mistake: Phoebe is going into the school in one scene, but as the camera moves she vanishes while on screen.
Character mistake: The first time Arnold tries Rhonda's marriage predictor test, he says his favorite number is five, but Rhonda actually makes six moves. The second time, Arnold says it's three, but Rhonda counts off four.
Revealing mistake: In Arnold's nightmare, when Bob points out that a stork is flying off their roof, his legs are incorrectly layered behind his cape. (00:12:50)
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.