I agree. According to FAR 37.103
(with no supplements in DFARS/AFAR), you do not have to prepare a Determination for the file for services that are clearly non-personal services. The written Determination is only required in "doubtful cases". But, its very appropriate for your contracting officer or policy shop to require a written memo in the file, prepared by the contracting specialist, describing why they determined the effort to be nonpersonal services. This would good training for the specialists and eliminate any risk of the "thinking" not being done.
37.103 -- Contracting Officer Responsibility.(a) The contracting officer is responsible for ensuring that a proposed contract for services is proper. For this purpose the contracting officer shall --
(1) Determine whether the proposed service is for a personal or nonpersonal services contract using the definitions in 2.101 and 37.101 and the guidelines in 37.104;
(2) In doubtful cases, obtain the review of legal counsel; and
(3) Document the file (except as provided in paragraph (b) of this section) with --
(i) The opinion of legal counsel, if any,
(ii) A memorandum of the facts and rationale supporting the conclusion that the contract does not violate the provisions in 37.104(b), and
(iii) Any further documentation that the contracting agency may require.covered by a delegation of authority.