If you're not pressing the clutch, then you can't blip the revs (the engine is connected to the wheels, so the blip has nowhere to go). I'm sure you understand that bit.
The touching the throttle (on the clutchless downshift) isn't to blip the revs, but to unload the dogs. In the few milliseconds the shift takes you either hope the revs are close enough for the dogs to engage (and hope it doesn't snatch the rear wheels), or your force it in and lock your wheels, or you get a horrid grinding noise as your dogs get smaller, and the oil in your 'box get's slightly more metally. But if successful (which with close gearing and race rubber it usually is) it's a very quick way to shift gear.
However, using the clutch will provide a time to blip the throttle, allowing dogs, engine, wheels and the road to all be going at the same speed, and thus being easier on everything (and not spinning you round as much). A good jab on the clutch, with a nice big heel&toe movement, will see a lovely gearchange nearly every time, with very little time penalty.
I think that's right. Correct me if I'm not.