If Shawn had any doubts about how much his mother still wanted him around, or if there were any question in his mind about whether or not the man she married truly WANTED Shawn as a son, even if they had been discussing the step-father's adoption of the boy, the perp could easily have exploited that.
Devlin could have heard on the news, after taking Shawn, about the mother and step-father and worked on the boy's mind, feeding him doubts to the point where the kid could have been largely convinced they wouldn't care if he never came back, and thus never tried to get away. But he might still have had some lingering doubt; maybe that's the reason behind the cryptic question on the Foundation's blog asking when they would stop looking for their son.
Yes...this is something that we may find out...I guess during a trial, maybe...what this Devlin guy did to keep Shawn with him all of these years...
It would seem that the lingering doubt is OVER. Craig Akers indicated in the press conference that Shawn initiated the request to continue the adoption. Mr. Akers also indicated to the press that to "not be surprised if Shawn will soon go by the name of Shawn Akers" (paraphrasing a bit here).
I agree completely with your analysis.