I think it's more akin to renting a coffee machine. I ring Virgin Coffee Machines up to tell them to take their machine back as their new price is too expensive. Their retention rep then says "Mr. Game, you're such a valued customer, we'd hate to lose your custom, I've spoken to my boss and we can give you a discount and hold you at that price for life". Customer retained, rep meets his retention targets and gets his bonus.
Virgin Coffee Machines accept this discounted price for the first year then contact me and tell me the "for life" contract was only for a year, and the machine rental price is going up again. Had I known that I would have switched to Eircoffee the last time around, who had a particularly attractive offer at the time, even though I prefer the way Virgin deliver their coffee beans.
If I was also free to end the "for life" contract after a year, it's probably not enforceable. And even if enforceable, probably not worth my while paying a solicitor. But I'd feel free to keep the machine and keep paying the discounted price, until they turn up to collect it. Of course if the coffee machine breaks or I want to upgrade to the latest superduper Highspeed Fibreground Coffee Machine, I'd expect them not to honour the discount.