Yes you are absolutely right. My idea was to give players the ability to freeze a reel after each round. This turned out to be unintuitive. If you freeze a 7 you actually do not improve your average payout (because now you can only win with two more sevens) and the dominant strategy would be to freeze a cherry each round. This kinda felt boring to me so I left it out.
And yes a winter themed machine would have worked as well ;)