I've made an image comparison between the shots from that Star Wars Blu-ray Up Close at LucasFilm: Part 3 of 3 and the HDTV-broadcast, and guess what? Nothing has changed, except for a little more brightness (and even that done so badly, the black bars aren't black anymore, but dark grey). For a better comparison I've also brightened up the HDTV-shots, and they look almost the same after that:
TESB 1: Blu-ray (?) / HDTV / HDTV (levels changed by me)
TESB 2: Blu-ray (?) / HDTV / HDTV (levels changed by me)
TESB 3: Blu-ray (?) / HDTV / HDTV (levels changed by me)
ROTJ 1: Blu-ray (?) / HDTV / HDTV (levels changed by me)
ROTJ 2: Blu-ray (?) / HDTV / HDTV (levels changed by me)
ROTJ 3: Blu-ray (?) / HDTV / HDTV (levels changed by me)
ROTJ 4: Blu-ray (?) / HDTV / HDTV (levels changed by me)
Just open them in different browser tabs and compare.
The article specifically mentions that Lucasfilm wants them to be called "HD Stills"... not "Blu-ray Screenshots" or anything, so maybe they're still not finished doing the color corrections? On the other hand it's pretty stupid to promote a Blu-ray with stills that don't represent the product...