One could argue that it is the presence of structures with quantification rather than the topic-focus articulation of the quoted examples that is responsible for the indicated semantic distinction.
the Praguian writings from the sixties convincingly demonstrate that it is not difficult to find sentences without quantification that exhibit the same phenomenon (for reasons I will mention in a minute, in the examples, the capitals indicate the intonation center): Russian is spoken in SIBERIA versus In Siberia, RUSSIAN is spoken, or John works on his dissertation on WEEKENDS versus On weekends, John works on his DISSERTATION.