So a witch is going to be psychic just because he or she is a human. But what I think you mean is do witches have to be more psychic than non witches?
Witches do not necessarily have greater psychic powers than your milkman. But what they do have is an awareness of the powers they possess and an understanding of how to use them. Take me for example, I am probably the least psychically gifted female in my immediate bloodline but as I use and develop the limited psychic powers I do have I will get more results than my more gifted relatives who choose not to utilise the potentially greater powers that they have.
A good witch will work with her natural abilities. A psychic witch may well use spirit communications in many of her workings, a less psychic witch like myself may be more concerned with energy generation and personal will (I've got will in spades....).
A lot of the witches I know will understand and harness their personal strengths and in many cases, perhaps surprisingly, these strengths do not include particularly developed psychic powers.
Image http://www.sxc.hu/photo/1388426 (Vieran2001)