Playing Spot the Difference between the two pages, the new one lists the publisher as Bethesda rather than Activision. Developer id Software was acquired by Bethesda's parent company Zenimax in June 2009, just a few weeks after Wolfenstein 3D came to XBLM and PSN. Also, the release date is now listed as May 31 of this year, which is a bit odd. The box art is slightly different too, and once more notes Bethesda's name instead of Activision's.
Overall, the whole thing's as curious as Adolf Hitler in a mech suit. The timing's certainly interesting given the recent reveal of Wolfenstein: The New Order. When approached on the matter, a company spokesperson told Joystiq, "No comment on that from Bethesda."
Update: Bethesda VP of PR and Marketing Pete Hines told Joystiq there's nothing to see here.
"No changes. Was originally published through Activision, so now that it's reverted back to us we have to jump through ESRB (ratings go to the publisher, they don't "follow" the game to a new publisher) and console hoops (game has to be "re-certed" by the new publisher)," Hines said.