In my opinion BPEL can do more than Interconnect.
Yes they have overlap.
From my opinion Interconnect is used as a data-interface tool. where Bpel has more functions to create and start processes, work easily with services. Sure a data interface can be build in BPEL (the Oracle one to be specific), and there should be nothing wrong with it.
And from a support point of view you want to have 1 tool to maintain instead of 2.
My guess is that Interconnect, and the solutions build with it, will eventually dissapear into the BPEL process manager.