One of the main advantages of being a champion is enjoying the customary championship advantage in a match - giving the champion the freedom to lose a match either by disqualification or countout and keep the championship in tact. Obviously many champions have taken advantage of this fact, and there's been several instances of them purposely getting disqualified or counted out to keep the title in the easiest possible way. In order to punish those that take the easy way out, there's been instances of match stipulations where the champion would lose if counted out or disqualified. One such instance came during a quite excellent feud in 2011 between Randy Orton & Christian. Orton had beaten Christian for the World title, but Christian earned another rematch, with the added stipulation that if Orton was disqualified, or the refereeing wasn't up to scratch, Christian would automatically become champion. Christian spent most of the match trying to rile Orton to lose his temper and get himself disqualified. Christian even invited to hit him with a chair, but Orton resisted. Eventually Christian's plan worked after he spat in Orton's face, who in retaliation low-blowed Christian, and lost the title by doing so. There's dispute about whether this ruling should stay in effect and titles should be lost by DQ or countout, but there's the chance of interference, and being disqualified without it being the champion's own fault. Given the response to Orton losing the title in that fashion, it's unlikely to change.
