You are right that the police shouldn't react the way they often do to one of these calls. However with the kid having done 29 of these calls (that we know about) there's no way he wasn't aware of what the police might do. He was likely counting on the police to over react which he got off on.
After all where is the fun in making a call to the police only to have them knock on the door and have a polite conversation with the home owner before leaving. He wanted the police to do more or else he wouldn't have kept trying to swat people. Was he hoping for a murder by cop? I don't know, but it certainly was a potential outcome of his continued calls.
As others have pointed out before they are US companies but they do lots of business in the UK. Hence there is the option for huge fines should Msft/ActiBliz go against this ruling. Of course the companies could decide to not do any business in the UK but that would also come at a huge cost. So, for the time being they will comply with the ruling while working to get the deal approved.
Where there's a will, there's a relative.