Interesting thread. I'll side with those that feel that "Obi-Wan" is rather a title than a name, especially since it resembles "Pada-Wan" quite a lot.

ANH established that Leia knew his real or adopted first name of "Ben".

That he adopted it before the time Luke (and Leia) were born could also be a gesture of huumility, i.e. that he himself felt he no longer deserved the title "Obi-Wan"- after his failure training Luke's father adequately to withstand the tempations of the Dark Side.

Addressing him as "Obi-Wan" in her holomessage I'd say by already doing that Leia made it clear that his capabilities as an "Obi-Wan" were absolutely necessary to see to it that the Death Star plans were safely delivered to Alderaan.

Anyway, I prefer to only refer to "Ben Kenobi", by sticking with his ANH name I believe I express sufficiently that I have no big love for the PT.