Sharon,
thanks for your feedback, however of course I had the idea of them being solid booked, but they do not offer any room for sale on any day after 10/1 that I checked, where other hotels in Munich offer their standard rates. So yes, at least the trade fair effect is to be ruled out.
As to not having called the hotel directly, I did discover this on a sunday evening, so my guess is that anybody on ft.com would be better informed than whoever I would have talked to at the Ren at that time of night...;-)!
Greetings - Dirk