In the US, "apartment" at least strongly implies rented. You'd normally say condo (or co-op) if you own. (ADDED: Or just "my place" or something like that generically.)
The terminology is a bit loose but it would probably be more customary to write "buy as many as nine additional units." If I invite you to "my apartment" the implication is that I'm renting although that's not an absolute.
Nothing. It's just that, in the US, when you're renting a unit that isn't a whole house, you tend to call it an apartment as opposed to something else. It's just conventional word usage at least today.
Does choosing a word that implies something not imply some kind of intent in wanting to have the receiver take something from what was implied?
Perhaps there is some kind of social embarrassment in renting and thus apartment owners have come to try and differentiate themselves by using what originated as a legal term?
