By not asking the entire 11th Circuit Court of Appeals to review an August decision by a smaller three-person panel that found the individual mandate component of Obamacare to be unconstitutional, the Justice Department signals that it soon intends to ask the Supreme Court to hear the case.
I may be misreading the situation, but I find that this is a reflection that the Obama administration is unsure of its re-election prospects. If Romney or Perry were to win the 2012 election, the best thing Obama could do would be to put the healthcare law before the Supreme Court while he was still in office, where he can exert political pressure to uphold the law and solidify his legacy. He might also feel that he needs to put his signature issue front and center to mobilize his liberal base just before the elections. If Obama were confident of re-election, it would make more sense to take this issue off the table now so that it does not unpredictably affect votes, and also to wait to see if he could get a bigger congressional majority in the 2012 elections.
On the other hand, one might think that someone confident of re-election might act the same way, because it doesn't matter then when the the health care issue is heard, and better to get it taken care of now.