A term for introductory phrases that qualify reality/veracity?

Solution 1:

They are pragmatic markers subclasses modality / veridicality (though Wikipedia still classes them as adverbs - even the multiword examples - at http://en.wiktionary.org/wiki/Category:English_modal_adverbs ).

Modality refers to the degree of confidence the speaker is claiming for the correctness of the matrix sentence (the main proposition) ("In my opinion," "Probably," "Possibly," "Obviously," "If I am not mistaken,"...; veridicality to the endorsement of the truth of the statement ("The truth is," "In fact," "Without question,"...).

There are other (sub)classes of pragmatic markers, and references to excellent articles can be found on this site.

See Swan at http://english-learners.com/wp-content/uploads/Language-Use-Grammar-Basics-for-Technical-Writers-Vocabulary-Building-Discourse-Markers.pdf (he uses the term 'discourse markers') and Fraser at the website indicated here: PRAGMATIC MARKERS - people on the Web at Boston University.

Solution 2:

In classical oratory, the Exordium refers to the beginning part of a discourse. The examples you cite are exordial phrases and are employed by the speaker to win the audience to his/her point of view.