Originally posted by Monroville:

"...who you think would have force sensed Luke in the first movie..."

I think that Vader was so consumed by his rage and determination to finally kill Obi-Wan that he was blinded/ignored everything else going on around him until after the job was done and he'd basked in his victory for a while. "This will be a day long remembered. It has seen the end of Kenobi. It will soon see the end of the rebellion."

Originally posted by professa:

"it will work
you need to look at it from the point of view of a first time viewer

the viewer would know obi-wan isn't telling the truth anyway, what's he supposed to say 'yeah luke, i killed your dad. you must come with me to alderaan'"

I think that that is a little to much credit to give to an audience. Especially a first time audience who would be watching the films in chronological order as Adywan intends. The sad fact is that a lot of people are dumb. Once they encounter that "A young Jedi named Darth Vader" point in ANH after having watched the PT, they would know that something was wrong but would not put in the extra mental effort to come to the conclusion that Obi-Wan is telling a little fib.