It's funny, I noticed the glass' potential for wiggle the moment I assembled the amp in all it's glory. It bugged me at first, but that glass block is just too damn beautiful-looking.
So beautiful in fact that I was willing to ignore the fact that the glass block is just ever so slightly wider than the aluminum case.
I suspect that adding an additional design element to hold the glass in place would take away from the simplicity of the design, ruining the overall aesthetics. Especially since the glass tends to reflect and magnify everything in an awesome way.
Most of the time, you'll never be touching the glass anyways, so it's a bit of a moot point. DEFINITELY not for portable use, if the weight of the thing didn't give that away already.