Is Hosted Anit-Spam/Spyware Limited to Protection to Threats from Cloud

For small businesses that do not have a lot of staff to implement and maintain an on-premise email and web presence solution, a hosted software solution (such as Postini and MXLogic) can make a lot of sense. I understand how hosted anti-spam, spy-ware and web presence solutions protect a network and devices from threats from the cloud, but how do these solutions protect the enterprise from threats carried via endpoints onto the network (i.e. removable drives, laptops, ftp, etc)?
Are there endpoint security products that complement the hosted solutions?