I'm at work, so I'll just do a list sans analysis.

- Straight characters in strong friendships
- Straight characters in uber-het contexts making light of slash (cf Brock in Venture Brothers, who is very very het yet exhibits exaggerated mothering and male camaraderie... not to mention the awful jokes)
- characters who are attracted yet suppressing
- characters who the author wants you to think are suppressing but are actually straight
- gay characters written by someone who views homosexuality as a deviation
- gay characters written by someone who views homosexuality as a lifestyle choice
- gay characters written by someone who views homosexuality as an orientation
- gay characters written by someone who views it as a combination of the above
- storylines which emphasize sexuality and deliberately *cough* screw with it
- storylines which are "asexual" and their relationships reflect that
- authors who want to capitalize on slash purely for the "weird" factor
- authors who genuinely like slash
- authors who tease, i.e. messing with perception is the priority
- authors who not only tease, but want their fandom to ignite (can we say Krycek?)
- cultural forces such as acceptance of and/or a stable role for ambiguous sexuality, as with many regions of Asia
- historical forces such as friendship / bonding genres
- authors who don't know about slash
- authors who view slash as a subset of ... slanting something (a character, storyline, etc) in favor of personal whims rather than narrative necessities
- authors who slash for aesthetic or personal purposes
- authors who slash to make a statement
-... or both
- slash authors using the storytelling components of slash in their original fiction
- authors who coincidentally use the storytelling components of slash without knowing slash

...now I have to get ready to leave work.