My Samsung box upgraded today - I totally agree with you. Picture quality on SD channels is now very grainy (significantly poorer) and there is also a reduction in HD picture quality too.
I have a Sony Z4500 and the picture with the old EPG HD box was fantastic on SD & breathtakingly good on HD. It now looks ok on HD and like an old CRT on SD.
This is very much a backward upgrade, a new EPG but at the cost of picture quality
I have sent a complaint to SKY, i'm not happy to continue paying them unless they resolve this (it truly is that much poorer) - I wait with baited breath . . . .