Anakin seems pretty P.O.'d at Obers at the end of ROTS. He even goes as far as to hiss out the words, "I hate you!" as he burns.
So we'll give ol' Georgy-poo the benefit of the doubt and say that Anakin is 100% justified in being "upset" with Obers for:
A) holding him back,
B) not getting him on the Council,
C) keeping him from saving mommie,
D) being too "overly critical,"
E) not trusting Palpatine
F) turning Padme against him (Anakin)
Okay, so nice list there, eh? So here's the question: if Anakin is this pi$4ed off at Obi the very last time he lays his beady little yellow eyes on him, then wouldn't we expect a far harsher reaction from Darth Vader when he realize that Obi Wan is on the Death Star in Episode IV? I mean, he doesn't lay out the fine china or anything, but he isn't exactly seething either. I mean, for cryin' out loud, Obers did all that stuff up above (A through F) and then cut his legs and other arm off! By Anakin's caliente mood, Obers might as well just have cut his wee-wee off too.
Sure, 20 years (or whatever the F'ck it is now) has gone by so maybe Vader has cooled off a bit, but looking back over their reunion tour on the Death Star, there is a sense of lingering "rage" that is missing given all that Obi apparently did to wrong our lil' Ani-poo.
The line's essentially go like this:
When I left you, I was but the learner. Now I am the Master.
Your powers are weak, old man!
You should not have come back!
Does Vader's reaction to Obi Wan in ANH seem far too tame to anyone else given all that Anakin has to apparently "hate" Obers for? No questions about Padme? No goading. No comments about getting left for dead on Mustafar. Nothing at all to "connect" the two trilogies together.