Perhaps they are re-sampling, upscaling, enhancing color and filtering to get rid of NTSC color artefacts, etc., contained in the original edited masters but they are almost certainly not re-mastering using the original sources or even submasters (such as might be done when re-mastering audio from the original multitrack master).
Here is the remastered Petty Free Fallin' and although it is presented at 1080 it is still 4:3 aspect and is clearly not at HD resolution; it looks very soft by today's standards.
To make things even worse, sometimes companies will even crop 4:3 footage to be 16:9, resulting in less things being visible than in the original.
Thankfully judging by the videos linked in the blog (at least the ones I've looked at), they've left the restored videos in 4:3.
For a good idea of how bad things can get when a company doing restoration messes with aspect ratios, this video highlights the bad restoration of Buffy the Vampire Slayer: