The Shatner-Uhura kiss was the first of it's kind (involuntary which leaves open the possibility that they both abhored the very idea), and the head turned to where the kiss was not visible.
Yes, those were the concessions they made to get it on the air at all, but that didn't make it any less controversial. And the network pushed for an alternate version where they didn't actually kiss, but Shatner and Nichols deliberately sabotaged every take of that version so they had to include the kiss.
As far as Davis and Sinatra, who's to say how friendly it was?
You can see it for yourself here:
Just a mutual peck on the cheek between two amiable colleagues. Davis and Sinatra were playing a photographer and his model in a musical sketch. There was nothing romantic about the scenario or the kiss.