You know the old saying about making assumptions...
Here's a strange thing to me. My girlfriend's name is Victoria. She goes by "Vickie", for short. Yes, it's a bit of an odd spelling with the "i.e."
Recently, Vickie has been the contact for some hiring. She's listed as Victoria. A few people e-mailed her for the position and addressed the first line to "Vicky". I am not really sure why people would assume that her name would be spelled that way. A Victoria can be Vicki, Vicky, Vikki, Vickie, Vikky or even Tori. And some just flat out preferred to be called Victoria.
Jobs are clearly in short supply, so maybe trying to go the personal touch is why a few of these people have done it this way. A couple of the folks who did this are acquaintances of mine who were probably trying to go for a personal touch. While they had never met Vickie, they were probably able to find out pretty easily she goes by the shorter version most of the time.
The problem is, when you're wrong, you're wrong, and asking around, it seems to be something people find personally offensive. You never want to make a mistake that jumps out at the person on the front page of a cover letter.