two words: telekinesis and levitation. most matured psychic pokemon are capable of doing these somewhat.

Not at all. I think it's cool that psychic types are able to float. I remember the FIRST psychic type I saw flying in the anime was Mewtwo. Second, was Alakazam. Third was Gothitelle (in the recent BW movie). But I don't think they are suppose to be able to fly in the games, though.

@LostOblivion I get what you mean. But do you think a Girafarig could float as well?

^ there is difference between flying and levitating, cba to explain it though. most are capable of it but due to game mechanics all would have to require the levitation ability to do it and that would close up a lot of strategies for them as a whole.

EDIT: 'most matured' I never said all of them are capable

Okay, but what about Dialga? Dialga doesn't seem to possess wings like Palkia. Is Dialga able to float because it's a dragon type?

Dialga is a temporal being and a pokemon deity, being able to float is most likely due to levitation a common method for wingless pokemon as well in other series.

I don't find it strange,mainly because of the fact Psychic pokemon can float because of telekinesis as well as levitation so I believe that's probably the main reason they float,I don't think that another Pokemon type can do that,unless it was part Psychic..or Ghost Pokemon can do it as well..well some like Ghost (Gastly)..then again I believe that's levitation or something like that ..well I'm pretty sure anyway..or I might be thinking of something else..but I don't think it's strange at all to see a Psychic Pokemon float.