That sucks, but I'm surprised a domain was available when the trademark wasn't - usually it's the other way around. What's worse than likelihood of confusion claims are dilution claims. For marks that are well known enough, there doesn't even need to be any kind relationship. Even a small plush toy manufacturer couldn't call themselves "Microsoft." This is why so many web companies go with neologisms.
I was surprised at first too, but after all this hassle it seems like one company with a domain name trademarked prevents others from buying domains that sound, are spelled, or are somewhat similar selling relatively similar products or services, so now I'm not so surprised.
I agree, dilution are an even bigger can of worms...
Here's a pretty good primer on trademark law: http://cyber.law.harvard.edu/metaschool/fisher/domain/tm.htm