Continuity mistake: In the scene where Dean uses the silver knife to cut his arm to prove he is not a shape shifter, a few moments later Dean is showing Bobby the hand print on his arm, and the cut is miraculously gone. (00:13:00 - 00:15:00)
Continuity mistake: When Sam approaches Pamela to give her a hug, you see his hand on her arm. In the next shot he is still walking towards to her and his arm is hanging at his side.
Other mistake: When the guy goes to room 1444, the door slams behind him. He doesn't even try to open the door. He just shakes the door knob.
Revealing mistake: The guy gets a pack of raw hamburger out of the fridge and starts shoveling it in his mouth. We can plainly see it's just red jello.
Continuity mistake: In this episode, Dean says he was born in 1979. In the first two seasons, in the flashback to their mother dying, that's in 1983 which would make Dean 4 years old. He's definitely not 4 years old in the flashbacks.
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.