I should also point out that I am not specifically arguing for the inclusion of Wavedashing and L-cancels in SSB4, just against the basic notion that it is undesirable for a game to have advanced techniques or secrets that require some work to learn and master.
I'll use Starcraft as an example again, although BW this time. BW was a game massively loved by casuals and competitive players alike, with one of the biggest competitive scenes in modern gaming. BW had advanced techniques such as magic boxing that you could not read in a manual, and that gave players who knew them an advantage. BW also had a thriving community for years, with many, many new players making the jump from "casual" to competitive player, and some rising all the way to the top.
You could say the same thing about bunny hopping in CS, or disjointing projectiles and transferring tower aggro in DotA, skiing in Tribes. All of these games had or have large fanbases, many of whom are casuals, and all of whose many competitive players were casuals at one point. The need to learn and perform techniques that a game did not instruct you on while holding your hand historically has not proven a significant barrier to creating a game with a thriving community of players who strive to improve.
If somebody has the desire to get good at a game, they will. If they're put off by losing a match to a guy who did a fancy trick, they were never serious about getting good to begin with.
The only real argument against good ATs is that they are unfair to players who do not know how to perform them and detract from pure proficiency using only the intended game mechanics. There is no solid proof to back up the fact that advanced techniques kill a game's community, and indeed the experience of many other games speaks to the opposite.