When Epicor moved from Vantage 6 to Vantage 8 (the predecessors to Epicor 9 and 10), they separated the UI from the business logic. Technically, the Customization is the method used to alter the behavior of the UI but that hasn’t stopped users from placing business logic there. The BPM process is the method for users to change the behavior of code at the server. Alternatively, one can purchase the SDK to get full control of server-side code.
The other reason not to put business logic in the UI is that other systems that interact with the business objects (WCF, REST, and even UBAQ) will not see the logic in a UI elsewhere.
Mark W.