According to the behind the scenes info I've read the coughing was Lucas, they put it in as a joke and he liked it, so it was kept. Did it remind him of Vader? Perhaps that's why it appealed to him.
In any case, now it's a similarity!
There's similarities between the prequels as well. Notice all the stuff that Anakin does in his ship in ROTS is similar to what he did in TPM (try spinning, that's a good trick! sneaking into the hangar past the shield). He also says "this is where the fun begins" which is Han Solo's line (can't recall if it was ESB or ANH, but one of those).
There's numerous references to Obi-Wans dislike of flying/space travel in AOTC & RotS. C-3PO says he'd forgotten how much he hated space travel in ANH.
Obi-Wan rides a shrieking creature (like the Taun Tauns of ESB), that's essentially a giant lizard (like the Dewbacks in ANH).