You are reading, Using icons in buttons – the Apple’s way.written on 11. February 2010
O, Hey…! I was fooling around something very seriously so didn’t mind anything happened around me. but now back into the loop 
came with something to show you and ask what you all are thinking about it. Designer, Apple Fan bois – This way.
I’ve compiled it as an image for ease, it must be loa…wait for it..ding.
Click for larger image
If it was a logical/technical error apple might have corrected it with iPad even if they couldn’t do it with iPhone 3Gs. That is why i posted it to my blog asking other designers like you, Why apple placed a White Square on that “Home” button of iPhone / iPod Touch and iPad.
They have used the standard icon on power button of all their devices – which re-designed many times, Never replaced them with the familiar home icon – allowing to distort the meaning.
But in the case of “Home Button” of iPhone/iPod/iPad they replaced the familiar home icon with a Stupid Square. Why ? Any clue ?
For your “clicking” pleasure, These are the links in the image : My Twitter , FeatherPot Website which is not open yet due to my laziness. And FeatherPot’s twitter account – active – shares useful links related to design and things a designer likes – that comes before me. 
Niyaz
One possible reason is that it will bring unwanted attention to the button. Apple did not want a “home” icon to be on the UI of their great product, especially because it is the only graphic on the face of the device.
If there is only one button, probably there is no need for a visual cue as to what the button does. People will figure that out anyway.
And the small square was probably placed there for any of the reasons:
1. to let you know that there is a botton
2. to let you know that it is a botton
3. to let you know which way to hold the device.
Of course all this is wild speculation.