Because if the government force Murdoch to sell those shares then you can bet any money the Sun, the News of the World and the Times will start a smear campaign against Labour. Just to teach them a lesson not to mess with the big Boys.

what happens if Sky don't comply? are there restrictions or fines or something that will be levied against them? will that cost more than the 200m loss, considering they'll probably just put up their prices to recoup the loss?

Given that Labour are currently unpopular, you'd have thought that the Sun and NoTW would already be on the bandwagon of slagging them off. If Murdoch thinks the Tories are likely to win then he'll switch sides again so as to be able to claim he helped them win.

Not that I read his papers or watch his TV anyway...

I can see the Government dragging their feet and having some long-running enquiry that goes nowhere, allowing Murdoch to get shot of his shares at his leisure to minimise any potential loss.