Judgement made in default != default judgement.
Default Judgement = the defense is a no show.
Judgement made in default = defense showed but stayed silent (or in the case of Spamhaus, walked out (= refused to answer) when the judge ruled that the court had jurisdiction)
Spamhaus/their lawyers f**ked up
How do you figure? Spamhaus (wisely, IMHO) looked at the case, decided they could spend boatloads of money fighting a frivolous lawsuit which they would *probably* -- but NOT necessarily -- win, or since they are not in the U.S.' jurisdiction, they could save themselves the worry and the stress by ignoring the lawsuit. The court that awarded the win to the spammer has no jurisdiction in the U.K. so as long as Spamhaus' CEO doesn't come to the U.S., what difference does it make to him? It's not like he's going to be extradited for this. If somebody sues me in a foreign country that I never intend to visit, the odds of me spending any money or effort to fight the lawsuit are somewhere between zero and none. Spamhaus did likewise.
Problem is Spamhaus originally appointed lawyers to go to the court. This was the mistake, when the lawyers appeared for Spamhaus, Spamhaus effectively 'appeared in court' (even if to contest jurisdiction). They should have, as you indicated you would (and as I would) not even appeared. If they had not appeared, then the CEO visiting the USA or not would have no effect as the case was heard in the Illinois court, and not in the federal court.
...the result was they had to pay a spammer for the f**kup.
Ummm, no. The result was a judge ordered them to pay a spammer for their strategic decision. It may be subtle, but there is a difference between a judge ordering you to do something and actually having to do it. As long as you are not in the judge's jurisdiction, you don't have to do anything they order.
Second issue in point, and a second mistake to make if you don't consult a lawyer. There is this little treaty with the UK, USA, Canada, Australia and most of Europe, known as the 'cross border enforcement treaty'. If you hold a judgement from a US court in your favour (not a default judgement - note the difference I mentioned above) against a UK entity you can apply to the UK High Court to have your judgement enforced, the ONLY defense against it is that the court where the case was heard did not have jurisdiction. Problem is Spamhaus worked out when it was too late that 'judgement in default' is not a 'default judgement' and therefore cross border enforcement would be applied. This is why they first tried to appeal the judgement (and were refused because they 'appeared') then appealed the amount of damages.
The simple facts were, they screwed up (they even admit it themselves that they "had advice which was incorrect") a judgement which is enforceable was made against them, they appealed on the only option - the amount of damages, and they won their appeal by having the damages reduced to $27k.
Net effect, they lost the case, they will pay or risk copping significantly more costs when/if it is brought to the UK high court for enforcement. That said, rumor has it, the game is not over, but only time will tell.
Note: this has been discussed to the death on NANAE where someone reportedly from Spamhaus responded with "please don't give the spammer ideas".