My question is this:
Why on some tv show opening credits do they list each cast member by actor name, and then list the final one “actor name as character name”?
Like on Buffy it goes something like, Starring Sarah Michelle Gellar, Alyson Hannigan, James Marsters, Michelle Trachtenberg, and Anthony Stewart Head as Giles…
I think Smallville does this too, aswell as loads of other shows. Any ideas?
By giving them a special credit, they are making it up to the person for the fact that they are listed last in the credits.
Cecil covered this here.
In case you read over it, as I did the first two times, Sauron is referring to this sentence:
I love “as” designations. It’s my best chance at learning a character’s name. 
You don’t even need the “as.” It’s considered a benefit to be listed as “and So-ann So.”
Thanks, now I know
This had been bugging me for ages…
Generally, your more veteran actors tend to be listed first, although that’s not always the case.
When Roman Holiday was being made, Gregory Peck, who almost always had (and has, probably), top billing (meaning, before the title), insisted that Audrey Hepburn-a then unknown Dutch actress-be given top billing along side him. The studio said he was nuts, because no one even knew who she was-but Peck insisted saying that she was the real star of the picture-not him.
Just one more reason to LOVE Greg Peck in my opinion!
Off to Cafe Society
Interpreting credits is an esoteric discipline that I’ve never mastered. I used to read the ER newsgroup and they’d have these 4,000 post threads that deconstructed the credits and what the place of each cast member meant.
I’ve heard that the specific place in the credits is one of the most hotly contested contract points in Hollywood, not far after compensation. Apparently either top billing or last billing (the “and Blank Blank as Blank” credit) are the most desirable, because most people remember the first and the last item in any given list.
jayjay
Phil Hartman got a lot of attention for taking the “and” role in News Radio.
Since the OP used Buffy as an example, I’m gonna run with that.
I suspect the “as Giles” was added to the opening sequence partly because he was the only adult in the core cast. In the episode-specific credits (whatever you call 'em) “as” has been used for the characters Spike, Drusilla, and Tara, who were sort of regulars but not included in the standard opening sequence.
The Sixth-Season use of “and Alyson Hannigan as Willow” is probably largely to the maintain the rhythm of the opening credits rather than just because of any profound wrangling on Aly’s part. However, there may have been some contention on whether it should have been “and Nicholas Brendon as Xander” instead. I haven’t heard anything on this.