It depends on the city. Montreal, being closer to being an European city than an American city, has a very good metal scene, for example. Nightwish had 2 sold out shows, fairly sure Stratovarius and Therion were sold out too.
I like Therion, one of my favorite bands (with Tristania and a few others, of course, it's hard to keep track these days). Went to the Montreal show, I honestly didn't expect it to be popular but the place was packed and the show was very good.
I understand a lot of European metal bands don't come to North America though... Therion hadn't been here in 7 years, and other bands like WT, Epica, (did Tristania ever come here?) might not feel it's a good investment (I don't blame them, as was said, most of North America likes old American metal bands).