Monica Bellucci, for better or worse, is seen in Hollywood as an exotic. You know, just as Penelope Cruz has been tapped to play Brazilian, Italian, Greek (ugh!) and whatever else, Hollywood filmmakers only see her in terms of filling whatever exotic roles they might have in scripts. Which aren't many. Your standard hollywood filmmaker doesn't know what to do with her. So while she may not be actively pursuing dumbass paycheck roles in movies such as Pearl Harbor, it's probably moot since those aren't really going to be offered to her. She's a fine actress and will be able to work in European cinema for a long time. Therefore, over time, her resume will be filled with a lot more Irreversibles than Matrices or Tears of Suns. Probably no way to know for sure, but I think her appearance in such tribe as Tears of the Sun demonstrates a willingness to do that stuff, but I don't think she even gets considered for most of that stuff.
Beckinsale, on the other hand, is not exotic at all. Even if she were to stick to the stage or try to only do British films, there's nothing about her that stands out. She's a decent actress, but there's not enough work in British film to sustain just a group of indistiguisible actress. If she wants to do any kind of substantial work, she needs to "go Hollywood."
Remember, though, it's not that I disagree with you about the point you're making about KB, or about Hollywood's siren call. I just think it applies to Monica as well. I won't go so far as to say "she would sell out if she could," but I think she's very receptive to siren call, but the call isn't really directed at her.
Incidentally, I have different expectations for Underworld. Not that it's going to be a great movie, but it looks like good clean fun. And I think it will be a boost for KB's career.