Playing around on tvtropes.com again, I was looking at Love Actually's entry, which resorted in looking at Keira Knightley's entry. She was listed as being a pettanko, which I had no idea what that was. Turns out, the pettanko entry defines it as a woman who is flat-chested and is a bit self-conscious about it. Then several examples are sited and THIS popped up:
"Keira Knightley.
In Pirates Of The Caribbean, her chest was made up to create the illusion of cleavage.
Which seemed to disappear in the later installments.
Captain Jack couldn't resist taking a shot, though:
Sparrow: "So unless you've got a rudder and a lot of sails hidden in that bodice—" (scans her briefly) "— unlikely..."
So is that a shot at her "smallness?" I never took it as such. The way he acts around her later on (and in our sparrabeth world) makes it seem like he doesn't seem to mind she's not as busty as he's used to. I always thought it was a shot at the fact she was walking around an island IN HER UNDERWEAR that, you know, was pretty revealing (for the time period).