Likewise for a new playing going into DotA - they'll have LoL, HoN, and for what it's worth, Demigod.
LOL@Demigod even being considered. It's DotA, LoL, and HoN.
Valve will succeed 100%. At least in destroying HoN. LoL will survive on the basis that its gameplay is slightly different, but more importantly, it's F2P. The original DotA will probably not survive, seeing as how its current maintainer is working for DOTA 2.
People keep ignoring the most important thing about this announcement: all of the Steamworks features Valve is building to accommodate DOTA 2. The number one problem with DotA and its spin offs have been the community surrounding that game. Because of the team nature of the gameplay, a bad player on your team means you lose the game. This causes nothing but rage and hatred. HoN and LoL both have matchmaking, but all that does is pair bad players with bad players and good players with good players, meaning the bad players will stay bad and will still rage.
Valve is adding in game training. Seriously, does no one else see how amazing this is? No longer are you scouring the internet for a guide. Someone can literally make a guide in game that you follow. Not only that, you can have a coach pointing things out to you while you play, and the coaches will get rewards for doing so. Community participation will tie into your in game rep. Things like that will actually give people an incentive to help each other out, something that has been sorely missing from the MOBA genre.
I don't know why everyone is so hung up on "Oh, it's the same game!" The same game that gets 6 million downloads the very day it releases a new version? Valve is fixing everything wrong AROUND that game. Nowhere to go but up.