League lacks a lot of skill-managing nuances that HoN and DOTA2 have, making the game much more newb friendly. The primary draw of the game genre is a wide variety of heroes that play differently and build differently, as well as gauging your ability to adapt and change builds according to the situation as needed. In HoN and DOTA2, this starts from literally prior to the first minute of gameplay. Most (if not all) heroes will probably need to choose their first skill based on the lane compositions and oppositions.
From what I've seen in pro games (ie, in large tournaments, etc) this kind of stuff doesn't exist in League. Every character has a "core" item build that you pretty much should ALWAYS get since it's optimal, and your skill build is pretty much set in stone; there's no reason to ever change your skill build as it won't affect your laning/whatever much at all.
I also want to point out that hero diversity isn't really a big factor in League. Either you're AP, AD, Support, or Tank, and you build your items as such. Sure you can try the occasional AP Master Yi in a pub, but no one seriously does that in high level games, unless they're just fooling around. In comparison, almost every hero in DOTA2 (idk about HoN, a lot of the new heroes are pretty similar..) have their own set role and excel at certain points... and are bad at other areas. Any hero in League can carry; some just happen to be slightly better at it. Not every hero in DOTA2 can carry, either because they lack the farming capabilities or because their skills don't help them carry in any way. (Trust me, I've tried to carry on Crystal Maiden.. Didn't work.)
Map awareness is also lessened in League because of the freely available wards. Your support can literally sit there and buy a ****ton of wards all game and ward the entire map, removing the need for any sort of map awareness on your part. On the other hand, the small input of a cooldown on buying wards (maximum 4 per 6 minutes, each last 6 minutes) means you can't do the same in DOTA; not to mention that they're more expensive (100 per).
Finally, adaptation to a game can literally start within the first 5 minutes of a lane. Heavy physical harass? Get a Stout Shield. Heavy magic harass? Grab a quick Cloak. This can mean the difference between getting EXP and Gold early game, and getting nothing at all. In League? Just farm till you build your core then adapt to whoever is most annoying on the enemy team.
This is heightened by the ability to deny creeps, which is a whole argument in itself, but I believe that it's an addition to the game which makes the game that much more challenging.