I'd like to take this opportunity to point out that anything you read on SPUF-TF2 should be taken with a grain (nay, a pile) of salt.
But yes, some people were angered about how a game they had paid for had become free (well, effectively $5), despite the facts that they'd had hundreds of hours to play it before, and it had been $5 during the Christmas sale and less than that during the first Haloween event.