I know exactly how they get that "peak" HP rating...you are partially correct in your idea of how they do it. However, they do not put a big flywheel on them, but they do put a frictional load on them to the point they stop turning. They don't measure any amount of torque or the like.
Something funny happens when an electric motor is stalled...it draws huge amounts of current and creates massive torque, especially in induction motors when the capacitors kick in (just like when you first flip the switch on). In the labs, they will literally stall a motor to the point it burns up and they read the maximum amperage drawn. They then do the math, just like you did, and give the "peak" HP rating based on that amperage draw.
What they don't tell you though is that your regular old house wiring will not supply that maximum amperage draw...because if it did, one of two things will happen, you will pop a breaker (which you may have noticed if you've ever stalled a good sized electric motor), or you'll be calling the fire department to put your house out.
So yes, while it is cheesy advertising claims, technically speaking, the motor IS capable of outputing that power, albeit under extreme conditions, only for a split second, and the motor will be no good once it does it.
It's about the same thing as saying my 360 cubic inch V-8 truck motor has a "peak" of 10,000 RPMs. So you put it in neutral, slam the gas pedal down and it winds up and hits 10,000 RPM's just as it disentigrates into tiny fragments....yep, the engine is toast, but hey, it made it to 10,000 RPM, if even only for a split second....same thing.
Many people don't realize just how powerful an electric motor can be. I saw a show a couple years ago on TLC and some guy built an electric powered drag bike. It had a single electric motor about the size of a 1HP induction motor, and it used an aweful lot of car batteries. It was capable of 165 MPH in the quarter mile. That sucker drew 900 amps when the rider cranked the "throttle". It was amazingly quite too
Sears is probably the worst retailer that harks those "peak" HP ratings. They do it on nearly every electric tool or appliance they sell.
The best way to rate a vac is by it's suction power, or "static pressure", not by how powerful its motor is, or is claimed to be.
Static pressure is measured in "inches or millimeters (mmH2O, or InH2O) of water", meaning that's how many inches or millimeters of water it could suck up into a calibrated tube and hold it there.
To kind of keep things on topic here in the computer world...some of you overclockers that have tinkered with cooling solutions may have noticed that larger fans on your heat sink don't necessarily translate into better cooling, even though the bigger fans may provide double or more the CFM of air flow....the reason is: static pressure of the fan
The fan needs sufficient static pressure to force the air down through the heatsink fins (it has to overcome the resistence of the fins...the "load"). Smaller, high RPM fans will provide more static pressure than a larger, slower turning fan, so they are better able to handle the "load" and get air moving through the heatsink (unfortunately, they are also a lot louder). It's a tradeoff really and you have to find the happy medium.
As an example:
A YS-Tech 92x32mm fan turns at 4,000 RPM and moves 73.3 CFM of air, but it only has a static pressure of 10.7 mmH2O.
On the other hand, the screamin 60x38mm Delta fan turns at 6800 RPM, moves only 38CFM of air, but has a static pressure of a whopping 21.1 mmH2O
Almost half the CFM of air moving ability as the YS-Tech, but nearly double the static pressure. Guess which one will cool a heatsink better?
