Then there were also the regulatory issues that the IBM+Sun deal would have faced. IBM and Sun are the main competitors in a few areas (large scale tape storage, for example). This would have made the deal more expensive for IBM than just the $7 billion price tag.

Oracle and Sun have very few overlapping markets (I can't think of any off hand, aside from the Oracle Red Hat clone and Solaris). As such, this deal will be much smoother for both parties.