I'd say it's a really selfish thing to do as well.
I've thought about it myself, and really, the impact it would have is one of two things keeping me here (the other being that I could be wrong about the future only bringing harder times). Sometimes, I feel dying in a car accident (ie, not my fault) would be the best way out. This opinion is still selfish, but if no-one knows about it, they can't blame me.
If someone close to me comitted suicide, I'd be annoyed at them for wasting the everything I've done for them. Afterall, it's pretty similar to being angry at someone who murdered this person, though probably leaving you feeling more guilty.
At least for me, there's enough distractions in the world to keep me going. Maybe because I'm not seriously suicidal.