When you go to a bank with a $1.00 dollar bill. They enter it into their system as $1.00. Say we call 0.0000000001 BTC, "1", if you take it to a bank, you hand them "1" and in their system it would still be entered 0.00000000001 BTC.

That can lead to a ton of manipulation. "Yes sir, you gave me 1, but the price of 1 has changed from 0.0000000001 to 0.00000000000000001"

$1.00 = $1.00
1BTC =/= 0.0000000001 BTC