Also on Spreadbet quotes you may find that the quote varies away from the 'mid point' based on the companies particular order book. If, for example on dow, a compnay finds itself with an increasing number of short positions it may start to lower its price in order to discourage any more sellers and attract a few more buyers which, the company hopes will balance out its overall position towards neutral. This is quite rare but it does happen mainly in quicker markets.
Hope this helps,
Steve.