It seems that many retailers have managed their stock better this year. Many of the big, multi brand calendars already offer exceptional value, so I think that they are generally very reluctant to offer further discounts. They can't be making a huge margin on these.
Also, reducing pisses off customers who have paid full price. I noticed on the Holland & Barrett reviews last year that loads of customers were complaining that they'd bought early paid full price!!
I think that last year was exceptional, as many retailers were caught out after high demand in previous years. Given that Harrods was released in August, it's still taken a long time to sell out, but they've managed their stock really well without it selling out too early.
I bought Harrods, Selfridges and Space NK as my main calendars for December, so slightly relieved that they weren't massively discounted, although I wasn't really expecting them to be.
There are still quite a lot in stock - Cult Beauty, Liberty, Harvey Nichols, Fortnum's, Sephora, John Lewis, NAP, Fenwicks, Elle, Mintd, Vogue, Flannels - so there's still a good chance of a last minute bargain!