SO has some more rigorous filtering of the front page so that it doesn't show ignored tags and prefers interesting tags. The idea being that they want to present a list of questions that are more interesting to the user. That, and just showing "latest" like the other SE sites would be a lot of noise due to the sheer amount of traffic they get.
http://blog.stackoverflow.com/2010/11/stack-overflow-homepage-changes/
So the reason you're seeing them here and not there is due to the filtering, unless you turned on that "hide ignored tags" flag that was brought up already.