Thanks for pointing that out. That was an old image which I migrated to S3 last weekend. Unfortunately the migration script seems to have many bugs in it; in that case the smaller versions did not get migrated. That is why it is not appearing. There is currently no easy solution to this so unless we uncover many such old threads I am going to have to leave them as-is. I am hoping one day that there are some reliable scripts to get the S3 migration done properly and once those exist I will be able to run them to fix these issues.
Note that any such error can always be fixed by hand if its your post -- download all the big images, edit the post, and re-add them where they were.
If we end up finding a lot more of these I will look into it more, it may be the script can be fixed without much work. If anyone else has found broken pictures recently please tack them on here for reference.