Strange duplicate choice in "open with" menu

I've had this issue with OS X for as long as I can remember. It seems to span reformats and installations (i.e., I've seen it on multiple installs). If there's a file I want to open, I'll right click and bring up the options menu, then choose the "open with" option. It gives you the list of recommended programs you can open the file with. The odd thing is that I've always had duplicates of Safari, Quicktime, Preview, and a few others on this list. There will be literally two Safari icons, both of which work find to open the file. Same goes for all other duplicates. Does anyone have an explanation for this?