Why is the BlackBerry better than Windows Mobile?

This is a serious question, not a product war.  I am not a Blackberry (BB) user so I really don't know.  For enterprise customers with Exchange, why would you pick a BB as your corporate standard over Exchange?  In addition for enterprise customers, why do consumers seem to flock to the BB as well?  I am really interested in your thoughts as to why the BB is better than Windows Mobile.