Changing Obi-wans line to Anakin would of course just be a matter of personal preference, without the PT i'd agree with you but in the context of the whole saga, from the viewers perspective, a lot of the OT doesn't make sense.

Vaders reveal in ESB will sadly be a surprise i think to very few individuals ever again.

Obi-wan's subtle reveal hints to the audience what we already know and what he wasn't ready to tell Luke. His current dialogue makes less sense if viewing 1-6 in order (perhaps he forgot his name he seems to have forgotten R2 and threepio!), but whether better or worse hardly disastrous.