I seriously doubt The Edge would use two delays in series. The first delay would also *delay* the second one:
-if first is set at, say, 450 ms, and the second at 600 ms, you'd hear a delay after 450ms and another after 1050 ms (450+600)…and any rhythm related calculation would be a mess. While having them in parallel makes things much easier.
I'm curious though. If you ever get a reply that makes sense I'd be willing to know about it.