Continuity mistake: Dean circles the newspaper article on Sophia Carlton. When he hands it to Sam the circle is different. (00:03:20)
Continuity mistake: When the Carlton son reaches in to pull the plug out of the sink you can see the plug chain on the cutting board to the left of the sink before he even reaches in, then he pulls it out and puts the plug chain on the board. (00:14:30)
Visible crew/equipment: Before The End of the episode, Sam and Dean are thanked by the sheriff's daughter and her son. When Sam and the mother are left alone, his microphone wire is visible when he stretches. (00:41:00)
Continuity mistake: When the girl is taking a bath, the water is so full that its almost overflowing. She gets into the tub and the water doesn't overflow. The faucet is still running and yet the water keeps changing from full to down below her shoulders.
Revealing mistake: When Sam pulls Angela out of the bathtub and on to the floor, you can see the panty line from the nude colored panties she's wearing to keep the show PG13.
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.