Heroes of Newerth went free-to-play back in June, and is now following DOTA 2‘s lead and making all its playable heroes free. Developers S2 Games have cited wanting to make all strategies, modes of play and options available to all players of their DOTA/MOBA/DOBA/MOTA-BOATA, so that no-one is limited by the smaller hero pool.
S2 also want to reduce pay-to-win scenarios and keep the game more competitive rather than biased toward those who can afford to buy the extra assets. So, if you’ve recently bought a bunch of heroes that are now free-to-own and are cursing the unfairness of the universe, worry not: any purchases made in the last 15 days will be refunded, and anyone that’s ever spent money in the store will be given a sweet new avatar. If you bought a bunch of heroes sixteen days ago, though, resume cursing.
Source: Heroes of Newerth Forums