Nah they're not important in pics... at least in comercial way..
I wonder if it has anything to do with the record label's pressure. (it seems that the usage of these promotional photos are strictly controlled by the record company)
Esp. if you look at the Ashes US edition, the original cover is pretty plain, so they put Vibeke's photo on the cardboard sleeve, as if the record label is afraid that no one knows Tristania has a pretty female vocalist. One might ask Why??? Not that I don't like Vibeke (I adore her), but that's not the point here. I suppose this kind of things the band has little control over it.
It is sad... but in the end, if it helps Tristania to breakthrough the market and reach more new audience,( and thus attract more people to this kind of music) it isn't such a bad thing, as long as the music is still good. After all, we are here for the music, not for their pretty faces or their images. I sure hope Tristania will keep experimenting, and releasing good records in the future, but without reasonable sales, that chance might be slim.
Sometimes it is naive to think musicians can make music without considering any commercial factor at all. Which band doesn't want to grow bigger? which musician doesn't want to make a living out of music and become a full time musician? I work full time and I draw at night, one day I hope to become a full time artist too but it's not that easy. Even if I don't want to do commerical art at all, I still have to think about marketing. How do I attract buyers and such. Even the least commerical artists would not hersitate to promote themselves using whatever means they can. If they don't, their galleries will or their work will hardly get any exposure.