Seems like LX and BA are now the only carriers charging for C seat reservation. Although BA charges for all, while LX seems to be limited to the throne. This is a new direction they are going and I have a feeling that these two airlines will very soon be joined by the rest of them.

Example : I was ready to pull the trigger on a BA C sale BKK-AMS at $ 1,500 a piece r/t. So for
two pax the total amounted to $ 3,000. But then add 400 Euros for seat reservation and it's about
a little less than an additional 15 percent. Of course you don't have to make a seat reservation and wait until T-24, but then sitting together as a couple or avoiding the two center seats in a 4 seat row is not guaranteed.