Wireless Network Signal Strength

Question

I use iwlist to check signal strength of local networks. The actual command I use is

 sudo iwlist wlan0 scan

To make the view a little simpler here (filter out irrelevant stuff), I will use

 sudo iwlist wlan0 scan | egrep '(Address: |ESSID:|Channel:|Frequency:|Quality=)'

When I run this command on my Raspberry Pi, this is the output that I get:

      Cell 01 - Address: 1C:**:**:**:**:**
                Channel:6
                Frequency:2.437 GHz (Channel 6)
                Quality=58/70  Signal level=-52 dBm  
                ESSID:"MOTOROLA-*****"
      Cell 02 - Address: 00:**:**:*:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=48/70  Signal level=-62 dBm  
                ESSID:"NSASA"
      Cell 03 - Address: 02:**:**:**:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=47/70  Signal level=-63 dBm  
                ESSID:"BroadbandHamnet-20-v3"
      Cell 04 - Address: BC:**:**:**:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=21/70  Signal level=-89 dBm  
                ESSID:"BillWhyTheScienceFi"
      Cell 05 - Address: C8:**:**:**:**:**
                Channel:3
                Frequency:2.422 GHz (Channel 3)
                Quality=20/70  Signal level=-90 dBm  
                ESSID:"Pepperland"

but on Ubuntu I get:

      Cell 01 - Address: 1C:**:**:**:**:**
                Channel:6
                Frequency:2.437 GHz (Channel 6)
                Quality=15/100  Signal level=15/100  
                ESSID:"MOTOROLA-*****"
      Cell 02 - Address: 00:**:**:*:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=15/100  Signal level=15/100  
                ESSID:"NSASA"
      Cell 03 - Address: 02:**:**:**:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=15/100  Signal level=15/100  
                ESSID:"BroadbandHamnet-20-v3"
      Cell 04 - Address: BC:**:**:**:**:**
                Channel:1
                Frequency:2.412 GHz (Channel 1)
                Quality=15/100  Signal level=15/100  
                ESSID:"BillWhyTheScienceFi"
      Cell 05 - Address: C8:**:**:**:**:**
                Channel:3
                Frequency:2.422 GHz (Channel 3)
                Quality=15/100  Signal level=15/100  
                ESSID:"Pepperland"

Notice that all signal strength are listed as "15/100" and there is no signal strength (dBm) being displayed.

Am I missing a setting or is Ubuntu not able to pull this information?