oh for goodness sake. The hijab was part of society long before islam was "born". The fashion of dressing in this way stems from the fact that women in this part of the world wore it when islam was born and so the trend has continued.
Without being blaspomous (sp) every religion will in certain ways be affected by the style of the culture that was around at that time, women were bought and sold back then and it was a very dangerous place to be.
why would you cover up in such hot weather conditions such as saudi? well if you went around dressed in hot pants and a bikini youd die of skin cancer, dehydration etc...The hijab as the turban (wrong word) that tribal middle eastern men wear is there to protect them from exposure to long periods under the sun and strong winds in the desert etc...
Islamic dress has taken on fashionably since then and now many muslim women wear it as asymbol and a form of identifying themselves as being part of muslim society. The niqab has absolutly no place in islamic dress, it came about post islam as part of the regime of much more extreme islam.
Did you know that in saudi they have added little foot notes in the qurans? they have added lines that comply with thier version of extremist islam, if i or you were to do this wed be stoned to death.