Now that we have your attention, are you ready to find out why you shouldn't believe those overhyped advertisements?
First off, those enticing "65% Off!", "70% Off!", and "80% Off!" ads generally refer to "discounts" off the highest-priced, most-restricted ticket classes (refundable, etc.). What the carriers are really saying is that there are cheaper flights out there than the most expensive tickets. News flash! In most cases, they're providing absolutely no support that any of those discounts exist under any circumstances.
Here's the bottom line: Most leisure travelers never actually buy the costliest, most-restricted tickets. Those are generally picked up by business travelers shopping on the company dime. With low-cost airlines, online travel agents, and flexible date searches all factoring in to your price hunting, it's rare that you'd ever pay the highest possible price anyway. So that 80% off "discount" doesn't apply to any flight you're likely to book.