I can tell you that even Charles Cook, the cook report has the 20th as "lean" republican. I suspect that they simply don't undertand these races and with limited staff are making educated guesses but will be proven way wrong.
I think these pundits are either inept or fraudulent.
Or Democrats. Oh, wait, you already said "inept or fraudulent".
I checked out Micheal Barone's Political Almanac from 2000 where Charlie Cook was a guest Predictor of Congressional races. He predicted in the 2000 cycle that David Minge(D) of MINN-2 and Sam Gunderson(D) of CONN-2 were both SAFE locks for Reelection in 2000. They both lost to Mark Kennedy and Rob Simmons in Blue states that voted big for Al Gore. It shows that House Contests are local. These GOP pickups saved the House for the GOP.