The difference is most likely on the "sending" spam end. What better metrics can be provided than "who blocks the most of our mail?".
It is interesting from the viewpoint of the spammer vs. regular guy. The spammer is going to tell you that delivering to yahoo is hard (I know, it sounds ridiculous) and hotmail seems to be very easy until you realize they are just throwing your email into nothing. If hotmail really thinks you are a spammer, they send you a "200 OK" response after you are done sending your message then they delete your message forever. Not to junk, not to inbox, you just don't make it in at all. This is a great way for them to manage spam because writing to /dev/null is something they don't mind doing for you. Gmail and yahoo tell you "No, you're a spammer, go away". Yahoo even tries to get tricky and sends temporary block messages regardless of who you are to see how many times you try to resend it.
Yes, I may have run a few too many email servers for too long.

Ok, I'll have my kids take their DS outside. Good idea. Tell them it's the law.

So, if I am hiding something, I am a terrorist. Well news for everyone: When you get uncomfortable because I am going through your underwear drawer, well maybe you shouldn't be wearing underwear you terrorist! What's the difference? I guess it's ok to lean over someone's shoulder and read as they write in their diary? If they don't want anyone to know that the person who smeared shit all over the walls of the bathroom was them, it's because they are terrorists. Though arguably in that particular scenario, I would have to agree.

I thought the Septims turned into dragon statues or something to stop infections.

They will always find some new way to send junk, and spamhaus doesn't usually affect the "big" email providers, they just scare ISP's into kicking people off their network.