1. Fine, fine. I'll rephrase. I feel that this "chunk" you speak of is not so integral to sales that Nintendo would pander to the smaller competitive demographic as some strange, circituous route to getting people to play the game.
2. It shouldn't be taken seriously. It's a game. I'm not saying agmes can't be competitive (otherwise you'll just drag out that tried and true sports analogy again) but, really, it's a GAME, and I'm not gonna' pretend it's anything more important than that.
3. I still don't follow your crazy theory that casual players are more likely to abandon forums, leaving them inactive wastelands, than competitive players. I could see this being SORT of true with only games like 64 and Melee. After all, without an onlien component, and without the competitive drive to gather on the tournament scene, they have much less to discuss. With the implementation of Wi-Fi for Brawl, though, I think you'll find many of the casual players sticking around to discuss their favourite characters, Subspace Emmisary events, complaints and praises for various game aspects, asking questions about unlockables, scheduling and discussing matches... Almost competitive behaviour, thoguh likely without the obsession toward utilizing exploits in the game, betting money, or to developing tier lists.
3. Regardless of the accuracy of my predictions, and your issues with my take on the controversial theory of "Smash Bros. not being serious bidness" or "casual players depending on competitive players for their continued enjoyment and Nintendo's continued success", the fact is that none of these ridiculously elaborate paths yoru logic is taking are likely the sort of thing to encourage Nintendo to ignore what seems to be generating the most praise and sales in exchange for attempting to create a deeper competitive scene. This is pretty evident from Sakurai's treatment of Brawl (slowing gameplay down to something between 64 and Melee, removing wavedashing and directional airdodging, fewer stages that seem tournament legal, an online mode that doesn't seem particularly friedly to online tournaments and the like and a similarly-treated spectator mode, etc.). The fact is that, regardless of which sect of Smash players you see as more worthy of the developer's attention, casual or competitive, it seems pretty clear that appealing to beginners and those that simply aren't quite as good (or quite as obsessive about developing the skills to become that good) has become Nintendo's marketing strategy, and their modus operandi in nearly all the games they are producing.
It simply makes more sense, and in many gamer's eyes, this treatment and how much the competitive players fret and worry and complain about it will not affect how "great" they perceive the game to be. Even the Melee reviews I've read on many sites seem to direct their praise at the ease of play in this franchise, and the general simplicity of gameplay. There really doesn't seem like any good reason for Nintendo to make the competitive scene one of their major priorities with Smash- they might include a few features and options geared toward it, but this is certainly not their main focus.