The possibility of Scotland voting for independence had that in spades; nobody really knew what it would entail.
Thus the media persisted in presenting it as a realistic, likely prospect, even when it was quite apparent (as per bookmakers odds) that a 'yes' vote was very unlikely.
What is an ideal amount of coverage on the negatives? Especially when the negatives of a No vote can be said and understood simply - Westminster keeps some control.
They were biased because they consistently took a negative stance towards the potential ramifications (not chance of outcome) of independence.