I appreciate the "better safe than sorry" advice, and I even cut out a reinforcement, but trust me, no extra support is necessary. I confirmed on a woodworking forum that that kind of joinery is much stronger than the cutaway 2x2 section, since it is all glued with the best quality wood glue and screwed. If you've ever tried to take apart something that was glued well, you'll find that the glue is stronger than the wood.
Also, note that the platform is screwed onto the top of the frame, which lends lots of horizontal strain relief, and also vertical.
Note that I don't require a running start, but just in case, I tried rocking on the bed, and couldn't get anything to budge.
It's funny that on the woodworking forum, several members thought I needed an additional support and leg in the middle of the bed, but with the 3/4 inch plywood, there's absolutely no sagging.
In any case, I'm all done, and I'm very happy with the result.
I decided to leave some space between the two pieces of plywood, to promote some additional air flow.
Thanks for the help.