The distinction between normal and heroic tier characters is not really "new"; it's actually one of the very original features of D&D that has been washed out of more recent editions
The technical definitions (insofar as we are concerned) are given here:
http://ddo.immersiveink.com/dd.html#normal-types
http://ddo.immersiveink.com/dd.html#heroic-types
and also
http://ddo.immersiveink.com/dd.html#superheroic-types
Basically, anyone with
fewer than 3 hit dice is "normal".
Anyone with
3 or more hit dice is "heroic".
Members of different classes will achieve heroic status at different levels based on the HD progression of their class. I.e., fighters are heroic at 3rd level, clerics and M-Us at 4th level, and thieves at 5th level.
In game terms, a heroes' exploits are generally known about and are the subject of gossip. A hero has something of a reputation in the game.
In terms of game mechanics, tier is quite important:
1) There are a bunch of spells that will affect normals and heroes differently. E.g., low level spells typically affect normals automatically but not heroes, or allow heroes a saving throw.
2) There are a bunch of monster abilities that affect only normals. E.g., ghoul paralysis doesn't affect heroes, dragon fear only affects normals, and so on.
3) There are a bunch of monsters that are not subject to normal missiles and/or normal weapons. As soon as a PC is heroic he overcomes this limitation.
4) It's also true that heroes are not subject to one attack (as a one hit die monster) per monster hit die each turn.
5) Additionally, normal types will always attack other normal types before they will attack heroes.
6) Finally, a character's attack matrix improves at each tier (see the coarse grained advancement on table 2.8
here).
It's also worth noting, perhaps, that the tier of a character is also a general guide as to the kinds of challenges that character is equipped to deal with. I.e., normals shouldn't expect to measure up to heroic challenges
[f=32]
Golgildir the Elf Medium (MV 12", AC 9, HD 1, hp 1/1, AL N) great cloak,
lantern; spells: color spray; scrolls: sleep, sleep, charm person
Hirelings: Georges;
torch[/f]