Companies should always be careful with contests and prize giveaway claims. Many businesses use lawyers to either draft, or at least review, any contest claims and giveaways. There are many laws that regulate contests and giveaways, so legal consultation would be imperative for a company to ensure it was in compliance.
Contests usually come with legally binding terms that apply to both the business and the contestant. Why not just state the terms and stick to them? If the business makes a false claim, it's subject to legal claims, and in a litigious society, those claims will be filed, whether really "justifiable" or not.
Yes, businesses should be careful about prize giveaways because so many of them appear to be scams. If there is some confusion in the fine print, a winner may demand more than he actually won. Everything should be run past the company's lawyer before the prize giveaway is made public.
If the business is honest and honors the rules that they set out and do not lie about the availability of the prizes they plan to give out they will be fine. But if the bank on the odds that no one will win the prize and do not make it available they can be sued.