Oh the S570 had and still has a fine Blu Ray picture. But the Direct mode feature on the S790 gives a somewhat to my eyes a better viewing experience. On the S570 there was only Standard, Bright or Theatre modes. I engaged it on Standard which may have added enhancements without my knowledge.
But you are absolutely right.Blu Ray is Blu Ray. As in what is on the disc is what is on the screen if no enhancements are added. Sadly with DVD players, the same cannot be said.
In an ideal world I would not be using DVD discs anymore. But so many films I enjoy have not been released on Blu Ray and will by now probably not get released in the formats lifetime. And some Blu Ray transfers are sadly sometimes worse than the previous DVD version.
A film like Bram Stoker's Dracula which has so many bad digital artifacts present on the Blu Ray Disc makes the Blu Ray upgrade pointless. Plus the black crush in the picture makes it unenjoyable to watch. And I doubt we will get another Blu Ray version of the film akin to the DVD of the late 1990's in terms of colour and look.
Finally I can watch it compression free on DVD with the S790 and get a close to Blu Ray quality. I always hated compression artifacts on a DVD especially noticeable on dark scenes.