If you consider the output "object code" there would be no need to edit, let alone roundtrip. You don't edit the object-code or byte-code from your compiler either.

At the SXSW Flash vs. Canvas panel it was mentioned that canvas has virtually no browser quirks; all browsers that implement it implement it correctly.

Naturally it's Adobe's job to handle the quirks when generating the output. I would be surprised, if forcing developers to edit generated code even crossed their minds. It just doesn't make any sense.