There are these nice and humble people who are ever willing to admit the possibility that they may not be infallible and can make be wrong sometimes - or so people say. If so, I am yet to come across one who says "I may be wrong but..". In the normal course, a person who seriously considers the possibility of his being wrong starts off diffidently saying things like, "Is it possible that.." or "Could it be this way?"
The most humble version of "I may be wrong ..." is the person who says that with the unsaid sub-text of "but I shall be very surprised if I am" and THAT is regardless of what he says after that.
There is also the bully's version of "I may be wrong..." where the sub-text is "but is there anyone here who dares to say so to my face?" (It sounds more emphatic in Hindi - "Kisi maike laal mein dum hai ...") Now that is a person who does not care two hoots about whether he is right or not but merely expects to be obeyed. That "I may be wrong .." here is a dare - it is not a statement of humility.
There is the "I may be wrong.." that expects the crowd around to say, "No, of course you are not Sir. How can you ever be wrong?" This is normally a boss who just loves his subordinates to be perpetually blinded by his own brilliance but does not feel brilliant unless they tell him so.
The ultimate is someone who says "I may be wrong..", expects it to be treated as the joke of the century and waits for his audience to have a hearty laugh. After all both he and they know that he cannot be wrong. Like, say, God saying, "I may be wrong.." when he is talking of how he created the world.
Hmm! I may be wrong in what I said above. (I know you are all laughing heartily at this statement)