I seem not to be able to select a paragraph and accept all changes within that paragraph. I work in Windows 8; Writer version 4.0.1
I think your observation is right. You can accept one by one or all.
But this could be an enhancement request. Please file on under:
and indicate it as an enhancement request,
A workaround is to open the Accept or Reject Changes window. Select their all changes for a paragraph (ctrl-key & click) and click then on Accept (not Accept All).