Nearly all manufacturers do not advertise/exhibit their product measurements? Why?

@waytoomuchstuff , I would add a third most important number,

3) Can I return my purchase after 30 days , no questions asked.

The reason for not providing infinite measurements from the manufacturers is a simple answer. Most engineers feel that non-engineers can't interpret the data. Secondly, the sales staff writes the specification, not the engineering department, pretty much useless unless independently measured. 

I understand a few measurements, but not most...I do not understand how any of the measurements relate to whether I will like the sound of the amp...

If you spend a lot of money on audio equipment, it is helpful to have a basic understanding of specifications and how those might affect successful partnering of equipment.  Examples include how the relationship between amplifier power and speaker sensitivity affects dynamic performance, as well as how input/output impedances, speaker phase angles, and impedance fluctuations with frequency, can affect the successful partnering between equipment.

I do not agree with the statement that specifications are "pretty much useless unless independently measured".  I cannot remember any cases I have seen with wholesale deviations between published specifications and published measurements by a third party, such as Stereophile.  I would not purchase expensive audio gear without reviewing the specifications as due diligence to verify the gear is likely to serve the intended purpose. 

Speaker manufacturers use measurements as a necessary tool in their development, but they're not necessarily to any good use to the buyer as it pertains to being a worthwhile reflection of their sound in certain respects. In some cases though they can be of use, like the measurements supplied to the pro compression drivers of my speakers where we used them as an outset (before taking measurements ourselves) for making filter notches and a peak suppression in an active configuration. The supplied measurements by the manufacturer turned out to be rather spot-on, we just used our own measurements to hone in more precisely on the specific notch and suppression frequencies in the tweaking process, while also to be the wiser on the actual, overall frequency response. 

What I would like to see supplied with speakers, and which I believe to be relatively indicative of a speaker's performance in selective areas, is distortion numbers at frequency intervals over their entire spectrum and at low to high SPL's. Distortion numbers in the bass for example can amount to double digits at higher SPL's, but the more headroom the lower the distortion and the cleaner the bass. The same essentially goes for the remainder of the frequency spectrum. At least in that regard - i.e.: distortion numbers - I see speaker manufacturers hiding the ugly facts from exposition here, rather than honestly feeling them "irrelevant" to the consumers.