Photobucket are within their rights to do this but it is really sad that so much of the message board culture is inaccessible because popular free image hosts tend to go away after a few years. I would lay money that 90% of posts over 10 years old have broken images.

The moral of the story is for forums to host images themselves, but nobody wants to do that because:

a) uploading files is annoying to implement and exposes the forum to security issues

b) storing the files can take a huge amount of disk space

c) serving the files can take a huge amount of bandwidth

d) the first message board to allow uploading files would just become a huge dumping ground of images for other boards to link to, necessitating implementing a referer block just like Photobucket

Personally I think that the message board developers have really dropped the ball by refusing to implement a really bullet-proof solution into their software by default. It is a hard problem but the only real solution is to host the images yourself. Third-parties are always going to let you down eventually because their goals do not align with yours.