I noticed the same thing. In fact, even outside of their listed offers, if you punch in your desired dates through the TR portal, you'll often find free nights. (Granted, most of my weekend free rooms were for the Imperial Palace, but still...)

In my case, my previous trips have been either DT or at MGM properties. I haven't stayed at a Harrah's property in 5 years, and had minimal action on my TR account - probably less than yours. I played at the KC Harrah's for maybe 30 minutes earlier this summer. Go figure.

Anyway, last trip, my MGM comp came up one day short, so I booked a free room at Harrah's LV for one night. I didn't have to pay a dime - exactly as promised. No strings attached.

I've seen postings on a TR-specific board suggesting that, by racking up 600 pts. in a single session ($3K cash-through in a slot - expected loss $200-300), you can get all the free rooms you want for years to come through the TR portal. Other postings suggest that Harrah's lowers the comp bar for customers with "home casinos" away from LV, trying to get them to fill rooms in Vegas.