Interestingly enough there have been 7 occasions where someone has become a World Champion in WWE without actually winning the title in a match...
1963: Buddy Rogers is announced as winning a tournament in Rio De Janeiro to become the first WWWF Champion (the tournament didn't actually happen and Rogers was just made the first champion)
1997: Vince McMahon ends the match between Bret Hart and Shawn Michaels and gives the title to Michaels. Also known as the "Montreal Screw Job".
1998: In a worked angle referencing the previous year's events, Vince McMahon stops the match between The Rock and Mankind and gives Rock the vacant WWF(E) Championship
2002: Brock Lesnar refuses to defend the WWE (Undisputed) Championship on Raw, so Eric Bischoff creates the World Heavyweight Championship and awards it to Triple H.
2006: Rob Van Dam cashes in his MITB briefcase and defeats John Cena to win the WWE Championship. The following evening Paul Heyman presents him with the newly reactivated ECW Championship.
2007: John Cena is injured, the WWE Championship is vacated and Vince McMahon awards it to Randy Orton.
2011: Edge uses the Spear in a match against Dolph Ziggler and is stripped of the title. The World Heavyweight Championship is then presented to Dolph Ziggler.
The WWE Championship has never changed hands more than 3 times in one night. This has only happened once at No Mercy 2007. The title was vacated because John Cena had to take time out due to injury. Randy Orton was then awarded the title, lost it to Triple H who then lost it back to Orton in the main event of the card.
There are only two people in the WWE who have held all 3 "World Championships" (WWE, World Heavyweight and ECW Championships). They are Kane and CM Punk.
No one has held the "big 3" (WWE, ECW and WCW) of championships, not in the proper sense anyway. In order to have held the "big 3", you would have had to work for each of the promotions and been champion during a time when they weren't inactive or owned by WWE. Despite this, Big Show is the one who has come closest. He has won the WCW World Heavyweight Championship whilst being a part of WCW, the WWE Championship and the ECW Championship during it's revival by WWE. There is no one who can become a "big 3" champion, unless WWE was to sell the rights to ECW and WCW and the two companies were restarted with their original titles intact.