I think dex adds to ranged attacks as Str adds to melee attacks.
Str doesn't add to melee attacks, neither does Dex to ranged. Sorry for absence much worse internet connection than expected. Will be back to normal in 48hrs.Originally I thought so too. It's a d20 standard. But under the Ability score explanations it doesn't say that. Strength only adds to damage for Melee and Thrown Weapons.
There is no mention of bonuses applied for Attack for either ability. Same thing for Dex bonuses adding to Dodge Defense, it's not there either. Other than skills and Reflex saves, Dexterity doesn't do as much as I am used to.
Where's WD? He might be able to clear this up.
CHANGES TO ABILITIES
• Strength and Dexterity: Strength and Dexterity in Mutants & Masterminds
do not directly influence a character’s chances to hit in combat, and
Dexterity doesn’t improve a character’s Defense score. These capabilities
are purchased separately with attack and defense bonus. This brings the
value of Strength and Dexterity in line with the other abilities and allows
players to fine-tune their characters’ combat abilities (so not all strong
heroes are good melee combatants, for example). If you want a character
whose great Strength or Dexterity provides combat ability, simply buy the
character’s attack and defense bonus in proportion to those ability scores.
On the other hand, you can also have a strong or dexterous character
who’s not especially good in a fight, if you prefer.
• Intelligence: Unlike other d20-based games, your Mutants & Masterminds
character’s Intelligence modifier does not alter the number of skill points
your hero gets. In Mutants & Masterminds, skill ranks are purchased with
power points, just like everything else.
DODGE BONUS
Half your defense bonus (rounded down) is a dodge bonus, which is lost
under certain circumstances, such as when you are stunned, flat-footed,
surprise-attacked, or otherwise unable to defend yourself normally. Other
circumstances—such as when you are helpless—cause you to lose your
entire defense bonus, and may apply additional penalties to your defense.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.