Abdications are more common in some countries than others. For example, most monarchs of the Netherlands abdicate. While, most monarchs in Great Britain reign until the pass away. It all depends on the country and the situation.
For King Albert II, he decided to abdicate because he turned 80 last month and he questions how well his health is. Most of the time, the cause is because of age.
Also, the Emir of Qatar, Sheikh Hamad bin Khalifa al-Thani has abdicated in favor of his son the Crown Prince, Sheikh Tamim bin Hamad al-Thani.
It's not certain how many more Abdications will be this year (or how soon any other ones will happen). We'll just have to find out.
2013: The year of Abdications!