In both the DSG and the WSG, proficiency checks are ability checks; in other words, you roll a d20 and are successful if the roll is lower than the ability score that governs that action.
In both, there is an automatic failure range for the check. In both, proficiencies apply modifiers to the check. In both, the modifiers become larger when the players spends a proficiency slot to improve a non-weapon proficiency. But in all three of these cases, the specifics for DSG proficiency checks are quite different than the WSG.
- Automatic Failure: WSG= 19-20. DSG= 1-3.
- Modifiers: WSG= TN+modifier (success more likely.) DSG= d20+modifier (success less likely.)
- Proficiency Slots: DSG= add +2 to roll per extra slot (higher proficiency = success less likely.)