I thought about this a lot this morning at church. Oddly enough, the reading today was about the Jews having to choose between the gods of the Ammorites and the True God.
I would doubt, first of all, that either of the two journalists was a practicing Christian (most journalists aren't, regardless of who they work for) so in a sense, they weren't rejecting their Christian faith, specifically.
But in the eyes of the Muslims, they were doing just that, because the Muslims regard the West as synonymous with Judaism/Christianity, so the Muzzies got the propaganda value they wanted out of it, and the ME has just become much more dangerous for all. This won't be the last of these kidnappings for forced conversion (propaganda) purposes.
In terms of the early Christian martyrs, there was serious debate in the early Church over whether Christians who had apostasized could be forgiven and welcomed back. It was decided that they could be, although of course they had to do penance.
Fortunately, most martyrs realized the importance of what they were saying and doing and did not apostasize, or, as you say, there would have been no Christianity. Words and gestures are our way of communicating our interior disposition to the world; interestingly, what the reporters said was not considered binding by them, but obviously was considered so by their captors.
Good points you make. Thanks for sharing them.