ADSL broadband risk to business

Do business managers that use ADSL broadband for their internet connectivity understand the potential business downtime and the risks involved? In our experience small businesses often use ADSL broadband services as their only internet connection. However as this does not come with a service level agreement (SLA) from BT, and SMTP email can be difficult to re-route quickly, do the business owners really understand the risk to the business should the broadband be down for an extended period of time?