For me, the inability to separate strategic from tactical seems to be a given, but I can decompose that into some lower level assumptions.

1) Tactical decisions must be made in line with strategic goals.
2) Tactical directions must be interpretted through an understanding of the strategic goals.
3) Strategic direction must be based on what is tactically possible and feasible.

I am not saying that outsourcing is impossible to do well, but that it is quite difficult to do well and the answer is not rely on SLAs and management controls. Probably the most widely discussed manufacturing outsourcing arrangement is the Toyota production system. Toyota is well known for its high degree of integration with and knowledge sharing with its key suppliers. Toyota has been successful due to its emphasis and coupling strategic and tactical issues. I will also heartily concur that most businesses and their IT departments fall woefully short of this level of integration.

The decision to outsource IT is largely based on the current poor alignment between IT departments and business. The belief is not that outsourcing will improve IT services, but rather that IT service cannot get much worse and we might save a few direct dollars as well.

Communication and information sharing are keys to any business and these are the areas where IT is supposed to provide benefit. Few companies are actually leveraging IT for business benefit and that trend is unlikely to be improved by outsourcing IT. Better integration of IT and business is what is needed.