Sorry guys. I was absolutely incorrect. The OT did NOT get a 4K scan for the Blu set, and it's Lucas' fault. According to secrethistoryofstarwars.com, when commenting on Lowry's work for the Blu release:
"Sound and Vision also questioned John Lowry about the unusual low-resolution of the release, a decision made by Lucasfilm and not his company, but he rather dodged the issue by alleging that the opticals were at less than 4K due to generational loss, but surmised that Lucas might re-do the entire process for an HD release. As it turns out, he hasn't, as the film has been shown many times on HD broadcasts using the HD master, although a re-do for Blu-Ray seems possible but unlikely."
Here are some additional comments:
"...the [Episode IV] negative was scanned only in HD resolution of 1080p, in 10-bit RGB.  This was a state worse than the primitive 2K scans ILM had done for the SE. By contrast, when Blade Runner was restored and enhanced in 2007, the live-action was scanned at 4K, the normal standard, and the visual effect shots at 8K. Godfather's 2008 restoration was scanned at 4K for the entire film, while Wizard of Oz's 2009 release was done at 8K. Why Lucas chose to source his master from a paltry 1080 HD scan is hard to fathom, especially when 4K was long in place as the standard, with 6K and 8K looming on the horizon as a viable replacement since data storage was becoming cheaper. One reason may be because Lucas was shooting the two prequels--Attack of the Clones and Revenge of the Sith--on the Sony CineAlta, which itself was 1080 (being the first generation of HD feature-film cameras). This is another undoable element of the prequels--filmed on 1080p HD, they have, at the most, less than half the resolution of the 35mm original trilogy, with some arguing that 35mm resolves 5000 lines, meaning they have just under 1/5 the resolution (Phantom Menace was shot in 35mm, but then scanned in 2K--which is still an improvement over the following two films)..."
"[The 2004 DVD version as] released is a sloppy mess, in technical terms; blacks are crushed, colors bleed and pop distractingly, video noise is visible because of the oversaturation, skin tones are inconsistent and often very pink, scenes have weird casts to them (i.e. the Millennium Falcon scenes look very green), everything is much too dull and dim, contrast is not nominal, and many of the lightsaber effects are the wrong color (pink for Vader, green for Luke). The coloring is not even consistent with the prequels in some instances, whereas the originals were--for instance, the original blockade runner scene was meant to be Kubrick-esque bright white, while on the 2004 release it is a dull blue, yet strangely in Revenge of the Sith it is the bright white it is supposed to be. Lowry is often mistakenly pointed at as the culprits of these highly noticeable flaws, but in fact it is Lucas himself..."