^ As I understand it, it's more a case of the Blu Ray can't
have both, because the assets used for certain brand new special effects sequences in the DE were all done digitally, and those assets no longer exist so they'd have to spend money redoing them with new technology to make them match up to an HD standard. As opposed to the theatical cut, where they just need to run the original negative through a machine to scan it at a higher res. The simple fact is that no 'original negative' of the DE exists because it was an entirely digital production made specifically for the DVD era.
I assume the 'Special Longer Version' could
be done in HD however, because it was sourced from original assets that probably still exist in the vaults. It'd just be a case of tracking down the relevant negatives, scanning everything and then splicing it together to match the previous SLV.