I have to dis-agree with you, I work in Health Care and require encrypted email. They won't look at anything for email except BB. The iPhone is a great consumer model, but really doesn't meet the needs of most business customers. My 2 cents!!!
I work in the mental health field and my company uses enterprise email on the iPhone 4. There is nothing insecure about it.
However, BB has been in that market for years and is well established with a near-perfect reputation. So it is natural that people would gravitate to BB for secure email over Apple. But Apple is learning and improving enterprise with every major iOS update.