I'll take a stab at it (dons flame-resistant clothing)

Think of Va as the maximum speed at which you can safely stall an airplane without causing structural damage. If you try to stall the airplane flying faster than Va, you will physically break the airplane before reaching a stall (bad thing). During certification, these airplane-destroying forces are measured on the ELEVATOR. When you exceed Va, you risk tearing the airplane apart from control deflections that exceed those which the airplane is rated for.

Vno, on the other hand, has to do with wind gusts measured on the WINGS - NOT forces/structural limits on the elevator. This has to do with the wings getting all bent out of shape (literally) because of turbulent conditions suddenly producing damaging amounts of lift, stressing the wings. When you're flying fast, the wings are "working" with lots of air to produce lots of lift, and it you hit a sudden gust or patch of turbulence, the wings may suddenly find themselves "working with" more air than is structurally safe. When you exceed Vno, you risk causing structural damage because of a sudden gust of wind, rather than elevator/control deflection. This is why you only exceed Vno in smooth conditions, and only then, with extreme caution.

Think of Va as more of a control deflection issue, whereas Vno is more of an environmental/gust issue.

That theory may have a few leaks in it, but it's worked on a checkride or two.

Hope it helped!