Well, it didnt start that way, putting their big games, HL2 and tieing it to steam is what put it onto alot of computers.
The difference is, Valve tends to treat all the clients of its service fairly, that is those that sell on steam, you largely hear good news stories.
EA, or any big publisher, will only sell their games, and if they gain enough traction I am sure, will only sell their games on their own service.
The future of this scenario is bleak. A client for each publisher, with them setting the prices and sales and not facing any real competition with other publishers and titles in their own stores, each having their own 'community'.