Does the bonus action attacks from Martial Arts and Flurry of Blows add modifier to damage?

@JeremyECrawford do the bonus action attacks from Martial Arts and Flurry of Blows add modifier to dmg? Or are they like 2-weapon fighting?

— The Spicy Keychain (@OakForTheVines) April 28, 2016

When making a weapon attack, you add your ability modifier to the damage, unless a feature tells you not to. #DnD https://t.co/7Ds3Uklfo8

— Jeremy Crawford (@JeremyECrawford) May 3, 2016