Why can't a keyboard on the Samsung Galaxy S3 collect passwords?
As a programmer I find this interesting.  Password fields can be (and usually are) treated differently than normal text boxes.  Given that Android is open source I guess it's possible that Samsung has at least attempted to include code that prevents a password field from passing information typed in it back to the keyboard application, but like others have stated I am skeptical.  

In order for a keyboard application to collect your data it has to include the extra step of capturing your input, storing it somewhere, even if it's just temporarily in an instance variable, and then sending it on to a third party.  I would be interested to hear what Samsung says about this and how they supposedly prevent it, but I'm guessing that's an answer we aren't likely to get.