Thinner glass is available but just not from regular suppliers even green-house glass which used to be quite thin now has to be 4mm. There's a far greater chance of thinner glass breaking or cracking when being cut or in fact in use/storage.
It's a changing market a couple of years ago thinner glass was relatively easy to order from my local glass shop but his suppliers no longer sell anything less than 2mm.
I've found UK suppliers of thinner glass but it may be a case of minimum orders, buying as a business etc. I'll post back in this thread when I have details, meanwhile Ill check my plate holders.