回複：USCIS does send card via priority mail with - 回複：緊急求助：卡寄丟了怎麽辦

You are right and I just found USCIS changed their mail delivery serivce about 3 months ago.

See:

http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextchannel=68439c7755cb9010VgnVCM10000045f3d6a1RCRD&vgnextoid=79ecdd8ae14af210VgnVCM100000082ca60aRCRD