IDG Answers is a community of experts who are passionate about technology. Ask a question or answer one below.
You need BlackBerry Server 10 to run BlackBerry Balance, which is a new feature that enables BB10 users to easily keep their personal and professional data separate on their device (with help from IT). So even if you could run everything else on an older BB server, you wouldn't be able to use Balance, which probably is the main selling point to the enterprise.
Here's a rundown of how Balance works.