Remember, a broken image may not actually be broken. The links for these images are auto-generated based on the date and what the particular site is expecting. If a cartoon has not, for example been posted yet today, the image will probably look broken.
Also, some comics change between different graphics formats from time to time, possibly because of planetary alignments, possibly because it's just not their job to make my life easy. For those comics that do, I include an img tag for each standard format, which may result in some broken images even when the comic does show up.
