[Zope] zope da's

I have a few quick questions: why does zope use specific DA's instead of a common bridge like JDBC? I was apart of a web logic presentation a few weeks ago and alot of the developers liked the fact that a) they rewrote the socket/rmi api (it multiplexes n requests over a single socket), b) jdbc (of course!) exists and we could 'move this from platform to platform' and not break anything, c) scalability and clustering methods (they use master/slave stubs) which seems to be much more complex than ZEO- but it load balances at the service layer. any comments? but I am interested in the jdbc vs. custom built DA's george runyan grunyan@emerging.com