They usually follow through for some amount of time. This is because it takes time to figure out how they are going to absorb you. If they changed everything on day 1 it would be a cluster fuck. A simple example would be if Orcl bought a company that was 100% on SAP for financials. If all your SAP people walk out the door the first week how are you going to file the next quarter financials. So they claim that nothing is going to change and that the SAP people have nothing to worry about.