The question is was is more or less likely that warring parties would initiate such extermination campaigns in the 20th/21st century or in the 12th/13th (or any other period, say of length 100 years)?
That question I can't answer, but I can tell you I would be surprised if we are more likely to see such campaigns today than in the past. Since you have argued it was different in the past, do you have any stats to back that up? I'll do some googling later on this. It IS an interesting question no doubt.