No, that is incorrect. Like I said earlier, running a PSU past its rating, even if it can handle the load, will cause components inside it to operate outside their specifications, which will result in premature failure. If a PSU manufacturer could rate their PSU for a higher power output, then they would, because then they could make more profit, either from selling a more powerful PSU at the same price point as other lower-wattage units which would make them money from sales volume, or by raising the price along with the rating, which would make them money from the price premium they could charge for having a more powerful unit.
The real fact is that just because they can handle it, doesn't mean that they are designed to or that they can tolerate it for an extended period of time, which I have already explained more than once:
Well, yes and no to all of that. Saying that a PSU "can handle" a load isn't very clear. Does it mean that the PSU won't explode? Or does it mean that it will stay with the ATX standards? Or does it mean that it will go beyond the minimum and maintain extremely tight tolerances? Because where power regulation is concerned, a lot of "quality" comes from over-specing parts. Oversized capacitors and heatsinks, extra voltage regulators, stronger fans... you sum that kind of stuff together, and you can often choose between selling it as a premium mid-watt unit or a mid-level high-watt unit.What makes a quality PSU is that it can output its rated wattage while maintaining low levels of ripple and tight voltage regulation, among other things.
And the fact is, it's standard industry practice to use a single platform for a wide range of PSU ratings. A quick perusal of the UL certification directory will show this clearly. Perhaps the manufacturer simply underspeced a few components on a heavier platform for their weaker units. Or perhaps they changed nothing except the colour of the paint, banking on getting fewer RMA's down the road and a better reputation. Unless you specifically analyze each component, until you find the weak point, you can't know for certain that the PSU isn't capable of handling more than its marketed rating. But the fact is, a great deal of PSU "quality" comes from specifying higher-capacity components than strictly necessary.
And to address another point - it's a common used marketing tactic to sell similar items at different price points. The expensive unit commands a premium profit from those who can afford it, while the cheaper unit gets the sales from those who wouldn't have purchased the more expensive unit in the first place. Just look at how Intel bins their chips - lots of i7 920's that will do i7 975 speeds without any trouble at all. Which is why Intel never had a prayer of selling me a $1000+ chip under any circumstances, but they still managed to get $300 from me.