New Rules at Pokemon Tournament

That's all that's banned? I'm surprised Mewtwo isn't.

Interesting-- I wonder how this will affect the outcomes?

@Newten said:

"From my experience with the Pokemon games... downgrading the Pokemon to level 50 won't really make a difference, it just means anyone with Pokemon inbetween 50 and 100 can compete, but if they haven't been trained properly they will still be considerably weaker even at the same level, it's all to do with stats, and then there's strategy obviously. If there are people who've seen this news and think they have a better chance now, they're horribly wrong I think.  As for the Pokemon banned from use, those aren't the most powerful anyway, I'm pretty sure they just banned them so they won't have to go to all the trouble of checking if they are legit or not, all those Pokemon listed look like event Pokemon to me, in other words VERY hard to obtain. That's why they've done that.  If they were banning Pokemon to level the playing field they would be banning Mewtwo, Kyogre, Dialga, Lugia... that sort of thing.  So yeah, seems perfectly reasonable to me. "

Well besides Manaphy/Phione all the rest listed are event pokemon so ya it's quite possible that they may not be legit since some of them were either unavailable or just notoriously hard to get so people would use action replays and such to get a illiget copy. 
 
Also Newten is totally right a hardset level cap will not provide an advantage to novice players. This is because if someone is going to enter a competitive pokemon tourney of any large magnitude or among dedicated players than they will still be crushed if they don't know the mechanics. 
  
As said it's about min/maxing the stats on your pokemon so it fits the archetype you planned for it. Wether it's to provide a shield (high defense, special defense and HP) or a sweeper (high attack, high speed) and other such archetypes. Of course archetypes can be modified and obviously a player that knows what they are doing will make a balanced team so they can anticipate any varience their opponent will have.
 
To do this you have to get the right nature, IVs and EVs when training the pokemon. (nature and IVs are somewhat random but can be controlled to a significant degree by breeding and EVs are based on the pokemon you defeat while training) Along with this the actual moves you have taught or passed on to your pokemon (such as egg moves via breeding or chain-breeding) are very important along with it's type. (almost certainly want to have some that will give STAB [Same Type Attack Bonus] but being able to still be flexible*) 
 
The high end game competitive play in Pokemon actually gets fairly intense and unless you are playing against either someone that doesn't have the time(like me)/want to invest the time into the competitive scene or just doesn't care or is a total novice to the series that thinks they can just win via leveling and type differences than you will be crushed.
  
For anyone interested in finding out all about all the technical aspects of the game mechanics I would suggest heading over to Bulbapedia or Serebii or PKMN.net. Also on Bulbapedia you can find more indepth talk about the game mechanics of Pokemon if you so desire.

*for instance having a move that may not be the same type but will be super effective (2 to 4 times damage) against the type your pokemon is weak to may have so they won't be able to exploit that weakness.

You can't really prove that any of the Pokemon they will use are legit. Unless they are stupid hackers and don't input the right info for the summary.