Geez...someone might want to go watch the Andrew Ireland interview with Mike Sheahan. We had no money for Mitchell, plain and simple!
Was about to post the same thing. According to Ireland North's offer for Heeney meant the money available for Tom wasn't there as they paid more for Heeney than they were expecting to entering his 4th year and as Andrew said "In the words of Gil, you can't have everything". Basically it came down to the club deciding out of Tom, Heeney or Mills who they were willing to lose long term.