Why manufactures don´t burn in their amps and ...

I had to keep my lastest new car under 3K RPM's for the first 1K mile, and I like many others, I didn't like the OEM tires. Some manufacturers aren't convinced that power cords make much difference. For that matter, manufacturer's don't offer "...good (or the "right") interconnects or speaker cables.

I am a newbie wanna be audiophile so......

Personally, I don't believe that a power cord will make a detectable difference. I've never been able to detect one anyway. I've also never been to a hifi shop that has told me a different power cord will make a difference. Never had a dealer demonstrate different power cords. BTW, I'd love to be proved wrong!

The only cable I believe that makes a difference is speaker cable and that is barely detectable to my ears.

It's critically important to "burn in" any component.

The initial burn in period will just exceed the length of time during which you would have been allowed to return the component.

The remainder of the burn in period will just exceed the length of the manufacturers warrantee.

No conclusions should be drawn regarding the performance or reliability of any component until fully "burned in".

Shorter return periods, warrantees and/or egregious restocking fees will all shorten the length of time it takes to burn in a component.

Cost, pure and simple. If tubes are involved, the catch would be that 'used' would need to be put into the spec's.

With exception of speakers, the 'burn in' is a myth to get you into the rituals of the hobby. Double blind test, the only true way of telling, has proved time and time again it is not necessary.