For crying out loud! You're right.
Adding 16 will do the trick. Here's what those lines should have said:
// Nuclex.Graphics.Demo\Source\NuclexGraphicsDemo.cs, Line #42
this.primitiveBatch = new PrimitiveBatch<VertexPositionColor>(
I remember doing some last minute editing to revert things I had done in my working copy for testing. Obviously I reverted one line too much.
There's a new release available now, stripped from a clean checkout. Sorry to anyone who ran into this bug!