To address the issue RIM's Senior director for Enterprise Product Management Jeff Holleran, provided a full explanation as to why RIM is using the protocol on their current devices and their future BlackBerry 10 devices.
ActiveSync a matured protocol
So why ActiveSync? Holleran provides a number of reasons for RIM's use of the ActiveSync protocol, but perhaps the best reason is simply because it works. Yes, that's right, ActiveSync works. The protocol has been around since the early 90's and has been matured over time to a more robust data synchronization technology. This goes right along with RIM's ability to recognize mature technology that gets the job done. The company has been able to use ActiveSync to create a sync engine that works across all levels of messaging.
A single sync engine
Another reason Holleran gave was RIM's ability to create a single sync engine that would be able to reach more BlackBerry devices, instead of having just one solution using a BES. Using ActiveSync simply makes it easier for devices to connect to a mail server. Many devices besides BlackBerry use this protocol for that reason. This plug-and-play type connection makes it easier to connect to corporate mail server. Many times the user will find that the email setup is done automatically.
The decision to embrace the ActiveSync protocol is a smart move by RIM. It allows for better flexibility, scalability and a more practical use of a company's infrastructure.