They reckon "Times Online attracts the most insightful and informative reader comments from around the world", but that the change "unfortunately .. means that all old comments will disappear from the site."
So... they're about to throw away several years' worth of the world's best comments.
Losing content in this way is stupid. As well as losing all of this valuable (and free) content, they're also putting off people from commenting in future. Why bother if they're going to throw it away?
Would they go through the archive of the paper and delete all the letters to the editor because they were introducing a new format? No, people would think they were insane. Same here.