Previously there were rumors suggesting that BES 10 will not work with older BlackBerry devices meaning that administrators would have to run two versions of BES to cater to their users.
RIM's biggest market is among enterprise users, and RIM had to quickly respond to this rumors to avoid loosing more enterprise customers. The new-QNX based BlackBerry OS 10 will follow in the footsteps of the BlackBerry Playbook bringing BlackBerry devices into the future. With an innovative modern UI and promise of new powerful hardware.
source - CNET