It's normal for there to be constant power to the scanner. Here's the summary.
"The power switch was excluded because the scanner often acts as a pass-through device for a printer. When the scanner power is off, the printer will not function.
The scanner is Energy Star compliant and power consumption is only 8 watts in idle mode. Because the scanning bulb is only active during scanning, constant power to the scanner does not reduce the life span.
You can turn off the scanner by unplugging the power cord. However, this is not recommended. Microsoft(R) Windows might not respond when the computer is operated with the scanner unplugged"