Jesika,
The easy answer to why boys think it's so much fun is because they know it drives you crazy. The more you make a big deal of it, the funnier it is for them to "let one slip out" accidentally-on-purpose.
It sounds like maybe they are bored and tormenting you with these gas wars is a way for them to pass the time. If it's safe to do so, get them to play outside for a while. Let them rent a new video game (if you have a gaming system). It will give them something to do, both mentally and physically, and pre-occupy their brains with something other than gross farting contests.
By the way, is there something in their diets that's making them toot so much?? If you're not feeding them baked beans, cabbage, broccoli, brussels sprouts, etc... maybe they're lactose intolerant?? My youngest (a 9yo girl) used to have the loudest and most foul gaseous emissions (which she was extremely proud of, I might add....), and it drove me batty too. I just tried it for a week - reducing her dairy intake and not letting her have any carbonated drinks... (punishment for all the farting... but all those bubbles DO create gas) - and it worked!!
I still HATE it when hubby lets one loose under the covers and then fans the sheets.... I say, KEEP THAT STENCH WHERE IT IS.
Love, Scully