Sad to say,this has been on the cards for some time. There was never any doubt about sequels to Spider-man or Batman Begins, for example. Superman seemed to be followed by the pattern that also emerged after Ang Lee's Hulk. Rumour, rumour, less and less sign of movement, cast and crew moving onto other things ...
With the reboot proving successful for the Batman series, the Bond movies, though less so for Hulk, it's perhaps inevitable that WB would consider this approach for Superman. After all, SR, much as I like it, was an underperformer financially (people were expecting Spider-man like box office returns) and divided fans down the middle. You can never please everyone, but the movie never received the love that BB or Spider-man did. I think picking up where it left off (with a 10 year old Jason etc) might be a risky proposition. Ignoring that sort of baggage and delivering a more fun movie (like the Incredible Hulk) seems a lot safer.
Yeah as much as I'd love to see a followup to SR, and see the relationship with his son explored further, it's getting to the point where the kid actor is going to be too old to make the idea even worthwhile.
I mean there was already a big gap until Superman met him the FIRST time; by the time we get to continue the story, we'll be looking at a 10 or 11 year old version of that kid.