Ah yes, another scientific explanation that refuses to account for the possibility the value of the BTC itself goes up.
Not to say it would ever actually be worth it but the final number is completely false.
It doesn't refuse to account for the fact that BTC values might go up, it's just beyond the scope of that formula, it provides a comparison of the prices of mining your own coins versus buying them on the market.
If you mine coins now paying for electricity, you could instead spend the money for the electric bills on mtgox. Then if the value rises in the future you've made better profit than mining them yourself.