We can see all this in the account of the tiers of play (4e DMG, pp 146-47; very similar text can be found in the PHB, pp 28-29):
Heroic characters navigate dangerous terrain and explore haunted crypts, where they can expect to fight savage orcs, ferocious wolves, giant spiders, evil cultists, bloodthirsty ghouls, and shadar-kai assassins. If they face a dragon, it’s a young one that might still be searching for a lair and has not yet found its place in the world . . .
Paragon-level adventurers explore uncharted regions and delve long-forgotten dungeons, where they confront savage giants, ferocious hydras, fearless golems, evil yuan-ti, bloodthirsty vampires, crafty mind flayers, and drow assassins. They might face a powerful adult dragon that has established a lair and a role in the world. . . .
Epic characters traverse otherworldly realms and explore never-before-seen caverns of wonder, where they fight savage balor demons, abominations such as the ferocious tarrasque, mind flayer masterminds, terrible archdevils, bloodthirsty lich archmages, and even the gods themselves. The dragons they encounter are ancient wyrms of truly earth-shaking power, whose sleep troubles kingdoms and whose waking threatens existence.
When (for instance) paragon tier PCs confront a ghoul - which is of typical toughness for heroic tier PCs - that ghouls is not terribly tough. One well-placed blow (ie in mechanical terms, an attack that hits) will drop it.