Are integrated amps technically better than separates?

I would like to know why an integrated needs a separate power supply for the preamp and amp sections. My DAC puts out 4.2 v balanced which is more than enough to run an amp to full power. The pre and first stage amp sections are running at the same voltages. Isn’t my integrated pre section pretty much acting as a selector and volume control then?  I am using a Pass Int 250 which supposedly has a minimal preamp internally.
Enlighten me

I believe either topology can be as good as the other, it's just down to the price you want to pay for the functionality you need... personally I prefer separates. My preamp has inputs for MC (transformer) and MM cartridges, four other analogue inputs, a 64dB attenuator with 128 steps and four individually powered stereo pair outputs. That gives me the functionality I want with little compromise to quality. Actually, I think the volume control is a weak point in many amplifiers and a well implemented stepped attenuator can make a real difference on its own.

Ralph,

Would you fill in some of the details of what you know about power cords?  You've told us that a power cord that's not up to the job is going to hurt the sound, but what are the basic requirements for an adequate power cord?  One that will not degrade the sound in a system the average 'Goner might own.  

What impedance is adequate?  Should it be solid or stranded wire?  What gauge should it be?  What about dielectric materials?  As your system becomes more sophisticated, do you need a power cord to do more that deliver electricity?

I would greatly appreciate it if you can give us any guidelines or refer to where we can find answers to these questions.  This is one of the more confusing topics in audio for me, and one that seems to cause the most heated arguments.

I was not insinuating anyone's enjoyment of music is secondary. Just saying that it's not necessary to be a hardware hobbyist/tweaker to have a great sounding system to enjoy music.

Music enjoyment (while appreciating great sound - openness, detail, bass, clarity) is a separate area of interest to hardware, and people can make their own choice whether to have one or two hobbies. 

There are some that have a primary interest in hardware, some music and some both. Everyone is free to choose and spend accordingly. Personally, I have roughly equal investment in hardware versus software.