The images are (probably) hosted on Akamai servers.
Akamai is the bigest source for graphical ads (Flash and GIF) and many of the world's biggest websites use their services. If you are using an ad-blocker application (on individual PC's or at gateway/DNS level), it is most likely that their servers will be
targeted and the content from Akamai will be blocked.
As an example, I'll put the error that I've made some 2 years ago. Manually edititng the HOSTS file and adding fake IP addresses for Akamai servers blocked not only the commercials, but even part of Windows Update content.
Of course, I won't exclude a temporary DNS failure for Hotmail server responsible with those graphics.