The way I read it - it has been determined that there was no need for the original report since none of those entities had any obligation to report:
<<The Reporting Persons do not and have not beneficially owned 10% or more of any class of equity securities of Implant Sciences Corp registered pursuant to Section 12 of the Securities Exchange Act of 1934, as amended, and, accordingly, are not and have not been Section 16 Reporting Persons with respect to the Issuer. Accordingly, none of the Reporting Persons currently have or have had at any time from (and including) the date of the event reported on the Original Form 3, any obligation to report beneficial ownership on this Form, and the Form has been amended to so reflect. >>
I would ask: Has anything changed in substance? And why was the original reported if the answer is "no"?
It reads to me like there has not been a change in substance - "do not and have not beneficially owned" - and that they are just correcting a mistake with this amendment. Why they feel the need to do so? Maybe simply because it is the correct legal procedure when you find a mistake, and nothing more.