A little bit late, and probably have worked this out, however SalesLogix uses BDE as a layer in between SalesLogix and the Microsoft Database Communication layer. This is used in SalesLogix 6 as a direct communication cutting out BDE.
ODBC sits also on top of the Microsoft Database Communcation layer so both are near enough the same. However BDE can communication directly to this layer as well as to ODBC, so allowing a more open environment for development. So allowing communication with lots of different database and data sources.
The main reason why SalesLogix uses BDE as it also uses Delphi programming language, so you can write additional background scripts that get executed when updates / deletes etc... happen. So creating the tefs that are needed for synchronisation.