Reverting to SL can indeed be done, it requires that the hardware has not been set for the new OS. That is now the case.
What happened to me was my iMac had a graphics card go bad, among other things, Apple replaced it with an i5, came with Lion which I promptly wiped the drive, zeroed it and attempted to install SL. Guess what, I now had a brick.
So your claim that it can be done is half true. If the Mac came with Lion but the hardware is still SL then reverting is easy, if it came with Lion and the Lion hardware then you are stuck.
So you have it countless times is indeed possible but I can say with 100% certainty that an older OS cannot be installed on a machine that the hardware has been configured for the OS that came on it.
That means that 10.4 cannot be installed on a machine that came with SL, different hardware.
If you bought a Mac before November 2011 then you have a 50-50 chance of reverting, cut that number by the number of people that have a clue how to even start.
My beef, if you will, is that Apple is becoming a nannie, very distasteful in my view. If they want Lion to look like it does, I am ok with that, just give us the choice of color and function.
I have an iPhone, iPod Touch and an iPad 2, the iOS works flawlessly and that is where it belongs. My computers require a higher powered OS including color (which iOS has by the way) and functionality that Lion lacks.
But I am only one among many, Apple is leaving us old timers behind. Not a good idea IMO.