I don't have the rules in front of me to give you exact verbage, but light thrown should just be like other basic ranged attacks. Dex to hit and damage.
The whole thing only deals with Basic Ranged Attack. Normally, Ranged Basic Attack is a Dexterity attack that deals 1[W] + Dexterity modifier damage. The heavy thrown property allows you to replace Dexterity with Strength for this one attack.
You may have other powers that are Dexterity based... using a heavy thrown weapon with them has no effect. It only affects Ranged Basic Attacks, so that Strength based classes have a ranged option.