Agreed, a single melee character will probably find it difficult to deal with a flying creature, but an entire party ought to have some method to handle flyers that will vary from party to party. This may involve some of the following:
Magic items that have pull effects, cause a creature to approach you, or cause a flying creature to fall. Examples: grasping weapon (Level 6+), orb of indisputable gravity (Level 7+), skyrender weapon (Level 9+), magnetic armor (Level 9+), cherished ring (Level 14), ghost chain weapon (Level 25+).
Powers that have pull or slide effects, or teleport enemies.
Once the enemy is within melee range, powers and magic items that immobilize, restrain or stun can be used to keep it there.