This answer is only partially correct. The carbonyl carbon is electropositive since it is attached to a more electronegative atom and it also has positive character due to resonance. The bromine atom is electron withdrawing and thus the carbon atom to which it is attached is electropositive and is susceptible to nucleophilic attack.

The double bond is neither electron deficient nor is it attached to an electron withdrawing atom or group. Isolated alkenes are not susceptible to nucleophilic attack.