Obama’s nominees up to this point have been “conventional, qualified, and undramatic choices, who were named, at least in part, because they were seen as likely to be quickly confirmed.....

One White House official tells him, “Our strategy was to show that our judges could get Republican support.”

As to Sotomayor, Toobin points out Obama expected her to have bi-partisan appeal:

However, the positioning of Sonia Sotomayor, Obama’s recently confirmed appointee to the Supreme Court, as a judge who appreciates the importance of judicial restraint—historically, a cornerstone of the conservative idea of jurisprudence—not only indicates a desire for Republican support, but also reflects “an acknowledgement that conservative rhetoric, if not conservative views, had become the default mode for Supreme Court nominees.”

And, Toobin says, Obama is more focused on Congress than the judiciary as an agent of change:

Perhaps most important, though, Obama’s choice of nominees reveals his emphasis on using the legislative branch, rather than the judicial, to insure rights. In his own career, “Obama chose politics over law” as a vehicle for social change....In “The Audacity of Hope,” he wrote, “I wondered if, in our reliance on the courts to vindicate not only our rights but also our values, progressives had lost too much faith in democracy .

His conclusion:

"An Obama Court would almost certainly defer more to congressional and other legislative judgments....Liberals who once saw judges as the lone protectors of constitutional rights are now placing their hopes on elected politicians like Obama.”