I've Come To Suck Your Blood

So vampires and werewolves are immortal right? And that means they can never die right? Or at least not very easily. Depending on the author at hand they have any number of weaknesses, but generally they are immortal. So why is it that in the Underworld movies (which I do like, though #1 is the best), these bastards die so god damn easily? More so the vampires than the werewolves. Seriously these guys get a paper cut and they die. I mean in Interview With the Vampire, Lestat has his throat slit and he comes back and is still as much of a bad ass as before. But these guys? I mean they have all sorts of gadgets and vests and stuff, but they can't dispose of a werewolf or you know, stay undead. What.The.Fuck.
Another thing is the character of Marcus. He seems ruthless and bad ass, like Victor, but he gets killed by a helicopter? Did I type that right? Yes. Yes I did. Granted he had a wing shoved through his skull, but the helicopter finished the job. Also why is he the only one who can fly and turn into a bat thing? Speaking of Victor, his death is bizarre. In the first one he dies by getting his head sliced off, kinda makes sense kinda doesn't. Then in the third one which is a prequel he gets stabbed through the mouth...and dies. Then moments later is on a boat...alive.
I know I just spent the last 976 pages ranting about how these immortals really aren't immortal, and also pointing out plot holes, but I do really like those movies. I enjoy how they really aren't the pussy vampires that exist in the world of Twilight, but they seriously get a cold and die. I think the only other vampire character who was weaker in the end was Vlad Dracula in The Historian. Blah!