I have been suffering with this problem on my Retina Macbook Pro.
What seems to be the problem is DHCP allocation. My AirPort network is a little complicated, with lots of devices, and I think the AirPort Extreme was having problems allocating IP addresses.
I only did this this morning so I'm hoping it continues to work, but try manually allocating IP addresses for the machines you are having problems with to prevent DHCP messups.
Open AirPort Utility, select your base station and click Edit and go to Network.
Open System Preferences, go to Network and Wi-Fi in the side menu. Click Advanced, and go to TCP/IP
In AirPort Utility, create a DHCP reservation by pressing the +. Call the description the name of this computer, leave it on Reserve by MAC Address.
In System Preferences, select Configure IPv4: Using DHCP with manual address. Note your current IPv4 address and copy and paste it into AirPort Utility dialogue under IPv4 address. Get your MAC address by clicking the Wi-Fi tab in the System Preferences window, and copy and paste your "Wi-Fi Address".
Close, save, restart, etc.
In AirPort Utility you can add extras, so do it for all devices having problems.