That is true for the AR-15 blanks. I bought the AR-10 blank and with the use of the CNC machine, still came out cheaper than buying a ready to go lower receiver, if you factor in shipping, FFL fees and the like.
There were a few people there very vocal about having receivers that the .gov doesn't know about. A lot of talk about the ATF and registration lists. Some guys were a little overboard and their tin hats were a little tight. For me, it was a cheaper alternative for a hard to find lower receiver.