I agree. It doesn't seem fair at all. I can only think the reason big businesses are getting a free pass is because it is so easy for them to relocate elsewhere in the world these days. They can up sticks and relocate anywhere within a few months (or at least they CAN do, and so the threat is always there, whether they really would do it or not), which would have a devastating effect on employment and corporation tax (the ones that pay it, at least...).
Sadly, big business has got the govt by the short and curlies. This is not a new phenomenon and it certainly doesn't just boil down to the Tories scratching their rich mates' backs.