Valve have announced Dota 2 will be a free-to-play title at release. It is for this reason that Valve will offer a "Dota Store" that will only include "fancy gear to customize your heroes."
Due to fans suggestions in the games forums, Valve wanted to stress that "Dota 2 will not be a pay-to-win game. All the items in the store are cosmetic, and don't affect gameplay."
"All of the heroes will be available free of charge. We believe restricting player access to heroes could be destructive to game design, so it's something we plan to avoid," added the company.
Dota 2 has also been integrated with the Steam Workshop which will be a platform for artists to create new skins and artwork for characters, some of which may end up directly in the game.
Dota 2 will be coming out by the end of 2012. Valve will also be hosting an "International Dota 2 Championship" which will be held in Seattle, Washington on the 31st of August.
Source: Dota 2 Blog