I doubt that their API is spoken of as a liability internally because, if it was spoken of as a liability then Twitter.com itself is a liability. Why? Twitter.com itself is powered by their API[1]
It is spoken of internally as a liability, and the executives want nothing more than to get rid of it for many reasons, not the least of which being their current investors care only about user numbers, and don't seem to count third-party users.
Trust me on this.