This is supported by all major DBMSs, not just Oracle. The only exception is SQL Server, but it has a system stored procedure for this.

Also, it is not just a compatibility feature. It allows to:

• Avoid dropping and recreating an index just to add a comment;
• Avoid repeating a column definition just to add a comment: this is error prone;
• Avoid granting a user ALTER privilege just because we want it to be able to add comments;
• Similarly, avoid granting ALTER ROUTINE, that allows to change the SECURITY clause.

Dataedo CEO stated in a webinar that their tool doesn't add comments to MySQL because they don't want to use ALTER TABLE.