Tantrix: You should be proud doing so,since the money goes to the creators of the games
It's not correct, if one has limited amount of money and spends all on games. This way it doesn't matter if he'll buy 10 games on promo or 5 games during normal sale - same amount of money goes to the creator of the games.
It is also possible that they are just testing the engine of the website, and those games won't be on promo sale, I just noticed those games having red tag and lower price, while I was checking the bestselling games list.
I'm amazed how good Planescape Torment sales are - ot's already #22, and soon will probably be the GOG best selling game ever.