whew!  i have no clue who's rule that is, but it's definitely not one that i abide by :o
considering that the game has been in constant development for over 3 years, i can guarantee you that there's not another 2.5+ years of dev to go.  i'm gunning to pull this puppy to port in no more than a couple o' months.  start your stop watch and hold me to it ;)

I'd prefer not to time you, because I think it's a bad idea to release a game before it's ready and wouldn't want to encourage you to release it before it is.

More about the rule: http://en.wikipedia.org/wiki/Pareto_principle

I found it pretty accurate so far. For instance, I "finished" Immortal Defense in five weeks; it was feature complete at that time. It had all the levels, all the enemies, all the tower types, all the gameplay rules, etc. -- but it still took another four and a half months after that to get all the music etc. done and to finish up and polish it to my liking before release.

I generally do all that stuff as I go (i.e. as I work on things like levels and gameplay), so once I'm finished the gameplay, I'm finished with everything (and I pack it up and compile it in such haste and excitement that I inevitably forget to fix some errors I was putting off fixing). Maybe that's why I don't finish all the games I start - polishing is more fun than making in my opinion.