Every single question being asked here about what's different between Airport Extreme and Airport Express is clearly explained in a chart at:
http://www.apple.com/airportexpress/specs.html
For those that don't want to make the extra click, the answers are:
1 - They have the same range.
2 - They are both full routers.
3 - They both have printer ports.
4 - Express: WAN Port Only (*), Extreme: Separate WAN/LAN Ports
5 - Express: 10 Users Max., Extreme: 50 Users Max.
6 - Express: Audio Out Jack, Extreme: No Audio Out
7 - Express: No Modem, Extreme: Modem OR Power Over Ethernet
8 - Express: No External Antenna Port, Extreme: External Antenna Port
(*) = When used in Wireless Bridge Mode, the WAN port CAN be used as a LAN port to connect wired devices. (Computer, Video Game, or Hub) But that requires an ADDITIONAL wireless router.
Essentially, the simple answer is that unless you need more than 10 simultaneous users to connect at once, or a modem connection to the Internet, the Airport Express for $129 kicks the AE Extreme Basestation's butt now, in both price and features.
🙂