Felicity Huffman won the Emmy for two reasons:
1.) Among the three actresses for DH nommed, she's the most respected one having appearing in David Mamet plays and previously featured in a short-lived but critically acclaimed show, Sports Night.
2.) Among the Housewives, Huffman's character is the most sympathetic. She's not annoyingly ditzy like Susan, a control-freak like Bree, a slut like Edie or an adulterous gold-digger like Gabrielle. She's simply a mother who's trying her best to take care of her kids.