Question

in this link http://pokemondb.net/pokebase/32801/how-do-you-change-your-pokemons-ability-in-the-dream-world the answer is that a pokemon that apears in dream world has the dream world ability.so how can heatran have dream world ability when it is not one of the pokemons that we can catch or befriended in the dream world according to serebii.net http://serebii.net/blackwhite/dreamworldareas.shtml
are some of these pokemons that can't obtained in dream world but they have dream world ability has some events in dream world?

Answer 1

The Dream World abilities (aka "hidden" abilities) are ones that are programmed into the game. But that doesn't mean you can get every Pokemon with that ability. It all depends on when/if they ever release that Pokemon in the Dream World or via an event.

It may happen that in a future game they release more Pokemon or there is a method to get them, but for now you can't.