It doesn't take into account future increases in BTC value, either (which could offset this). There are many variables, but I for one think this is a useful tool for demonstrating that mining can be profitable.
Of course it is profitable (certainly if you already own hardware) but calculations without factoring difficulty increase are very misleading.
Of course it is profitable if the value of your earned BTC exceeds your hardware and electricity costs, but now we're venturing into the realm of tautology. It's not "of course" profitable for everyone, and reading the forum, many people are skeptical it can be profitable for anyone. Some simple math, and clearly it can. I gather that's why this calculator was made.