[Mr Popo]

The main difference is that league has very defined roles, mid late carry, offlane defensive carry, safe lane farming carry, jungle ganker, and safelane support. Dota all kindas of strats are viable: the most common strat, tri-safe lane; jungler with solo offlane; duo safe/off lanes; aggro try offlane; roamer with solo offlane; or duo-wisp mid.

Also in Dota there are 2 types of supports, and generally you pick one of each, offensive support and defensive support. The role of supports in dota is very different in that they are not just ward bitches, although the defensive support definitely is. The offensive support is usually a character with a very effective stun or nuke that does not need any farm to fight at level 1-3. Support is dota is a character that does not need much farm or exp to get online and do some work. They usually should be trying to shutdown or zone out the enemy offlane, while allowing the safelane carry to farm up his items. The safe lane carry differs from the mid role since the mid needs exp and farm to get online, the safe lane carry usually just needs $.

On the topic of junglers, seems this patch that junglers are really terrible if they cannot affect the lanes. The only way to get money out of the jungle this patch is to stack, and obv thats not a great jungling strat. The other thing is at your mmr people are a lot better about warding to block camps and get vision of the 20% health jungler creeping. Bad news, bad news.