Roberts was not filibustered and was confirmed 78-22. With Alito there was an attempted filibuster, but this was prevented by a cloture vote of 72-25 and he was confirmed 58-42. Obama did vote against confirmation in both cases and he also voted against cloture (for filibuster) of Alito.
Think you are right. In any case, filibustering is possible.
But Hatch is going ballistic about the mere mention of filibustering Kagan. Did he go ballistic about the possible filibuster of Roberts and Alito? Of course not.