Actually, the chance of each team making it to the CCG is below 12% because that equation would require several different factors than just number of teams and the final two slots.
For example, there are 7 playoff spots in each conference that would need to be calculated first.
Then you would also need to factor in 4 reserved division winner slots, 3 of which a team can never win regardless of their record.
Then you would have to factor in each playoff round and even if you ignore home team modifiers it would be a 50% chance per game once a team makes it into the playoffs while also reducing the size of the pool 2 times (wildcard + division round) from 7 teams down to the final 2 per conference.
To your point though, after 28 years, I don't care what the odds are, the Cowboys should have made it to the CCG at least once or twice.