I put these up for the same reason I put the Sky idents up. These are iconic idents that has created the image for Channel 4. These use CGI in a subtle way to create the the 4 in a split second in the ident. I think these work well because of the tension they build up before the quick reveal of the number. The satisfaction the audience get from seeing the for is why these are so popular. The viewer is glued to the idents until the reveal. The ads aren't tied to any programs in particular which means they can be used at random between programs giving the channel much more freedom.