I found this over at gamefaqs. While the information and discussion there is usually pretty terrible, I agree with every word this guy said :
Items: Tournament players choose not to use items mainly because of their random nature, also in melee items meant exploding boxes. Items can spawn at any time at any place, it isn’t that rare that an item interferes with an attack, it has happened to me at least a dozen times (yeah I’m kind of unlucky), the result is me being catapulted into the air because of some stupid crate or bobomb. Now think about this if you feel that items should still be used: By chance both players are far apart from each other just then a heart spawn next to the player with 150% the player picks it up and basically gets a free stock. Now the other player loses MONEY because of that situation. It is not possible to adapt to random, it doesn’t work that way, when money is on the line you don’t want something that is pure luck to affect it, when the option to take away the randomness is there (so don’t give me the poker garbage). Remember that most tournament players are of very equal skill and items can easily be game breaking.
Stages: Another controversial topic, I can’t understand why. Some levels force certain players to play a certain way, because another player has an advantage. Basically some stages give certain characters an advantage, that must be removed. Stages will always be banned before a character, why play a game where you can’t even use the person you want to use.
L cancel: the less controversial of the two well known advanced techniques. This has been in SSB and SSBM, this was very intentional, there was an update on the original SSB that showed exactly how to perform it and what it does, in the first game it remover pretty much all lag of an aerial attack, which lead to some insane combos. In SSBM it was kept in, most likely for the veterans of SSB who knew about L-Canceling already (Z-Canceling in SSB), however this time around it took out half of the lag caused by aerial attacks. This technique is in no way cheap and was intentional, it was most likely taken out of Brawl because the aerial attacks in Brawl do not have as much lag, and therefore was deemed unnecessary.
Wavedashing: The more controversial of the two well known advanced techniques ( I know there are many more, but these are the most talked about). This is not a glitch it is an EXPLOIT. Why? you may be asking yourself. I will explain. Every part of the wavedash was intentionally put in, heres the main parts: the jump and the air dodge was obviously intentional, the airdodge in any direction was intentional, the sliding animation of a character who dodges into the ground (notice the smoke around the character is different when compared to normal landing after a jump smoke). So every part of the technique can be used by any casual player and already is just not to the degree people took it. People have exploited this mechanism by constantly doing it over and over in order to achieve faster movement speed and use mind games. Was taken out of Brawl for a different form of airdodging, which i find interesting, being able to attack airdodge then attack is pretty cool.