I think the third car bit is in the team's commercial contracts with him, which remain confidential, so not part of the rules per se.
Personally, I'm ok with it. Comparing three drivers is little different to two. My real problem is that the sport seems to be matching inexorably to a full on spending war, driven by the structure of the commercial side, and that will limit innovation, and opportunity for the smaller team's, and that doesn't look like it will be fixed any time soon.
However, as long as after each race i can say "I enjoyed that" i will continue to watch. The rest is garnish.