The project task list allows a gantt view and can be used for status updates. Once the task is assigned, the assignee needs to provide regular status updates and update the task. With a regular comments field there is no time stamp and the user must just add comments to the task and remember not to remove old comments.
I actually solved this issue by creating two fields and a workflow in SharePoint designer.
I added one field for Current Comments, and another field for Comment History.
The Comment History was created with "Add to all content types" unchecked.
Then I created a list workflow with two steps that runs if Current Comments is not blank 1> Set Comments History equal to Comments History plus Current Comments. I also insert Modified (date) and Modified By (display name)
2> Set Current Comments to blank
The workflow runs on create or edit.
You could add a "comments" field - its built in to sharepoint and doesnt require workflows but is allowed to be append only so you cannot overwrite previous posters comments: see https://stackoverflow.com/questions/231529/comments-field-in-sharepoint-issue-tracking-list