It could be both mate. Even Technics dont have 100% accurate pitch control although its hardly noticeable on them. The reason for the record changing pitch now and again is becuase of wow and flutter I think. The more expensive the deck the less wow and flutter it shoud have. The cheapest decks have about 0.25% whereas techs have 0.01%
e.g look on the link below and you will see in the specs the wow and flutter:
DJ Store | DJ Equipment | Numark TT200 Direct Drive Turntable :: £164.00 