why balanced power last before component?

Atma, instead of being troubled or suspicious, neither of which sounds like fun; why not turn your 'concerns' into profit?
It sounds like you have a solution for which the need is there. People are obviously spending (wasting?) money on relatively expensive Equitech products to cure the problem-as you describe it. Why not earn good money by tutoring all the designers (you infer there are many) in what you have said is the relatively simple art of proper internal grounding? Or, offer a custom service of rectifying inadaquate/faulty grounding schemes in noisy amps? Since one can easily spend $3000+ for one of Equitech's balanced power products I'm confident many owners would prefer to pay you to fix the problem at the source.
Again, if you don't know how Equitech ( the only one I'm familiar with) balanced power solutions for AC current effect a very significant reduction in line borne power distortions-which benefits the power supplies of ALL audio gear transistor or tube- you may find reading the Equitech technical information to be enlightening. It's interesting you find the problem of AC line borne pollution/noise so simple. I quote ANGELO BAGGINI'S book-HANDBOOK OF POWER QUALITY- "power quality is apt to waiver". Seems to be a huge problem for many. Also, if MARTIN GLASBAND doesn't know about balanced power-I'd like to know who does.

Atma, as a follow up, in Baggini's book there is a section titled
MONITORING POWER QUALITY. In it Andreas Sumper & Samuel Galceran-Arellano open by stating "power quality phenomenon are physical phenomenon that, in many cases, are APPEARING AND DISAPPEARING ARBITRARILY (not based on reason or evidence)." This arbitrariness is something that definitely bothers lesser designers than yourself; so it looks like there is a profitable business opportunity; perhaps a global one. Best regards, Peter.

I have found that designers in this industry often do not like being told that they have introduced a bug in their product.

The way you ground audio equipment BTW is simple: the circuit ground in the gear is kept isolated and insulated from the chassis. This includes the input and output connections. The chassis is directly grounded to ground through the AC cord. The audio ground is then referenced to the chassis through a resistance, one that is large enough to prevent any significant ground currents. In this way the equipment will not put any current though the ground and will be immune to ground loops.

Its simple- not rocket science, but you would be amazed at how many designers have not sorted this out. As a result there is a lot of snake oil out there dealing with the aftermath of poor grounding, and its not limited to high end audio.

I use an isolation transformer (medical grade) from the wall before my Shunyata Triton. It greatly improves the sound of the Triton vs. taking the Triton directly from the wall.
09-20-14: Sabai

Medical grade? I assume the secondary of transformer is floating above ground, is that correct? In other words the two output leads of the secondary are Hot ungrounded leads. Neither lead has a reference to ground. One lead was not intentionally connected to ground making it the neutral conductor thus making the new separately derived power system a "Grounded AC Power System".

NEC calls this type of power system an "Isolated Power System".

If your medical grade isolation power transformer is indeed operating as an “Isolated Power System” You will not read a true 120V reading from either contact of the receptacle to ground. Danger Will Robinson!

Here is what Bill Whitlock has to say about a balanced power system.

Page 201
Quote:
Bill Whitlock, 9/4/2012 Overview of Audio System Grounding & Interfacing 201

So-Called “Balanced Power”

• Properly called SYMMETRICAL power
• Has very seductive intuitive appeal
• NOT similar to balanced audio lines in any way!
• Uses transformer having 120 V center-tapped secondary
• Both line and neutral output blades are energized at 60 V
• Although advertising often implies endorsement, NEC seriously restricts
its use – because it’s potentially dangerous!
• ONLY FOR PROFESSIONAL USE
• NOT to be used with lighting equipment, especially screw-base bulbs
• MUST have GFCI at outputs
• Only technical function is to reduce leakage currents
• Leakage currents are trivial system noise sources
• Reported noise reduction generally less than 10 dB
• Any real benefit likely due to its clustered outlets
This is an example of “marketing gone wild” if ever there was one!
End Quote
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
.