I am not sure where the article is now, but I remember reading that the current EK fleet plan includes replacement of around 68 of the older 330/340/777 fleet. Factor that into the planned aircraft delivery schedule and the total fleet growth is certainly less than the delivery numbers.
Below is a quote from Wikipedia:
"Emirates will begin phasing out 68 older widebodies – A330-200s, A340-300/500s and 777 “Classics from February 2011.
[91] Emirates plans to have over 320 aircraft by 2018, and some reports suggest that the airline will have more than 400 aircraft in its fleet by 2020.
[93]"
According to Wikipedia the existing fleet today is 144, with 196 orders. Thats a total of 272 aircraft, subtract out the 68 retirements and you have 272 aircraft.
In order to upgrade you need to double the existing fleet (if you were hired today) so 144 times 2 is 288 aircraft. The current plan of a 272 aircraft fleet comes up 16 aircraft short of that goal. All the above numbers come from Wikipedia, and as you can see there is a conflict between the quote above and the fleet numbers table on the same page in Wikipedia.
Remember, its aviation, and all the plans will change tomorrow.