Microsoft’s moving on to a new phase of its Windows ad campaign, and Jerry Seinfeld won’t be joining the adventure. A new series of ads premiering Thursday shifts to a more direct brand and product focus — a sharp change from the eccentric, image-oriented spots Seinfeld had helped orchestrate. In contrast to rumors circulating around the Web, though, Microsoft insists the transition has been part of the plan all along. The goal, the company says, was to reintroduce the brand and start conversations with the Seinfeld spots, then move on to more targeted territory.