The Whole Ten Yards--another cheap sequel I bought at the FAMILY DOLLAR (just like Lord of the Rings: The Return of the King and--you guessed it--THE MATRIX REVOLUTIONS)--was a relation of a rather ingenious situation.
Matthew Perry's character is just 'along for the ride' of Bruce Willis's hitman-character's fortune-plan.
While I'm sure The Whole Nine Yards was also a good movie, you don't need to have seen it to catch enough of its 'gist' leading into the plot of The Whole Ten ... i.e. The Whole Ten might hold some sort of "completion" of The Whole Nine, but you don't need to know that there was ever Nine to enjoy the Ten (unlike REVOLUTIONS, for which you need to have seen RELOADED to "get").