RPi2 USB power: is there a conclusive answer?

[A.T.E.]

Hi,
I know that this is probably hardware related, but still some of you could give a good advice or opinion.
I have been browsing the web, and I am seeing contradictory statements on non-powered USB HDDs:
One says that it should work if the power supply is 2A, if it is of a good quality and if one of these two lines (usb_max_power=1 or usb_max_current=1) is in the config file.
Another one says that it will not work, even with the best power supply, and that a powered USB hub is necessary.
In my case (RPi2 with XBian 20150407-0) I have tried to investigate the thing. I have run these commands:

Terminal

xbian@XBIAN ~ $ usb-devices | grep 'Product=\|MxPwr'
S: Product=DWC OTG Controller
C: #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=0mA
C: #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=2mA
C: #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=2mA
S: Product=External HDD
C: #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=2mA
xbian@XBIAN ~ $ lsusb -v 2>/dev/null | grep -e 'MaxPower' -e 'Bus [0-9]'
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp.
MaxPower 2mA
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MaxPower 0mA
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
MaxPower 2mA
Bus 001 Device 013: ID 1058:1003 Western Digital Technologies, Inc. Elements 100
MaxPower 2mA

I don't know what the "2mA" values mean here (if two Ampères are being provided by the power supply to the RPi2 or if there are two Ampères on the USB ports or only that these USB ports can supply up to two Ampères). So is this command output saying that the power supply is working as expected or not necessarily?
Then I added the below shown lines to the config, alternating the hash symbol on two different boots. But still I cannot use a non-powered HDD or CD-ROM (it's fine on a powered on a powered one, the above shown Western Digital, or on USB keys):

Terminal

xbian@XBIAN ~ $ less /boot/config.txt

#initramfs initramfs.gz 0x1000000
gpu_mem_1024=256
gpu_mem_512=144
gpu_mem_256=100
initial_turbo=3
hdmi_ignore_cec_init=1
disable_overscan=1
disable_splash=1
#usb_max_power=1
usb_max_current=1

What do you think?