I hate to bring up old posts... but heres my 2 cents...
I wouldn't really care if people used grenades... id probably prefer them in a more open area as i dont want one flying through the window of a 4ft by 4 ft mock house... However id still accept that as a kill too.
As for the aforementioned expectation of results... this is airsoft... Alot of times any sort of hit could be disputed, and you're gonna be let down at some point. If you miss, or the other person thinks they're still alive... Oh well, regardless of what you used your gonna have to keep trying. Alot of people expect to be completely safe during airsoft as well, and are letdown when an injury occurs, forgetting that they entered into a military simulation and are being shot at... You just have to learn to shrug things off and keep playing, what you perceive to be happening and how the other person perceives it are entirely different... perception is often not even close to reality.
In real life there are many stories about people laying flat within 5 to 10 feet of a grenade, on the ground, and coming out unscathed, as the blast "supposedly" goes up and out... One could argue that laying down negates a kill in airsoft then. However i would say the closer it was to me, the more likely it is im actually dead. I would give benefit of the doubt to the grenade thrower. You can usually always respawn anyways.
In short, i think if you got em, use em... and if your not happy with any of your results from any facet of airsoft, welcome to the real world, thats what you get for expectations... And if they arent allowed in a match, tough day for you, maybe next time. I dont think they should be disallowed, but i would never argue with the match rules.
As Hunter S Thompson would say "all energy flows according to the whims of the Great Magnet, what a fool i was to defy him"