I thought Jessica was fine in The Help. Far better in The Tree of Life. If she's nominated for The Help, I think it's more for her body of work this year. I didn't see that work in The Help as an award-worthy performance, either. She was very good, though.
As for the supporting vs. leading, you can blame all the "For Your Consideration" ads and screeners. They're the ones who plant the bug in the ears of the voters. There are no rules and nothing is mandatory. The Actors Branch gets a ballot with five blank lines on it for each category. They can write in whatever name they want, in whatever category they choose.
The only rule is that if an actor happens to get enough votes in BOTH leading and supporting categories, they can only receive the nomination in one. It's wherever they got the most votes. (You can thank Barry Fitzgerald for that, since he was nominated in both categories for the same performance in Going My Way--1944. They added that rule the next year.)
Jennifer Hudson, Tatum O'Neal, Haing S. Ngor, and several others have won supporting Oscars for (in my opinion) leading roles. On the flipside, David Niven, Nicole Kidman, Anthony Hopkins, and Luise Rainer (The Great Ziegfeld) have all won leading Oscars for (in my opinion) supporting performances.
I also remember the big push to get leading actress Susan Sarandon nominated for a supporting Oscar for Atlantic City. They ignored all the ads, and (to everyone's surprise) she received a nomination in the leading category anyway. So sometimes it doesn't work.
And sometimes it confuses voters, and the votes are split for a performance, unintentionally shutting them out.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22