Dunno about the interference. But USB hubs, gigabit switches, Wi-Fi devices, etc. often come in "plastic" cases. Do they use material with better RFI and EMI rejection(?) or does it affect them too?
I like the acrylic case. It looks like that's a bolt-on accessory suitable for the non-electronically inclined!
Oh it affects them too, if it matters to you. If I put my amp next to my DSL/router I can hear it (clicking) through my headphones even though WiFi is disabled.