Yes, your right, stickers do help to advertise etc etc but admins/mods/whoever have alot to do, arguably more important things to do with the running/up keep or the site. Am sure they wouldnt intentionally not send you a sticker but like i said - a simple PM or thread requesting it im sure would see it sorted.
I'm not sticking by anyones side or being biased because i could be seen as part or site staff. I, like yourself am just giving an opinion based on my experience...my experience being meeting some great people not only doing UK meets, but ones to Germany too, where the evenings in everyones company are just as good as the days driving