Newspaper publications are print publications and often must be printed for a specific amount of time, include certain statutorily required language, and the newspaper printing the publication are often required to be the "newspaper of record" associated with the contents of the notice; for real estate or individuals, it's often required that the newspaper be the paper of record for the county where the real property is located or where the individual in question is known to reside.
Online notices are supportive or additional notices for general public awareness and may also be required by law in certain jurisdictions. Third-party internet posting companies are not generally tied to specific county requirements as newspaper publishers are.