Only channels 36-48 available?

You may find that the utility program for whatever adapter you are using does not scan above a certain set of channels.
Almost certainly the base station is making the appropriate channels available, but you aren't 'seeing' them.
You could try using a third party scanning utility like Network Stumbler or similar to see if your adapter will look that far out.

In Europe, the available channels in the 5 GHz radio band are: 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, & 140.

The 802.11n AirPort Extreme Base Station (AEBSn) can only provide a subset of those, namely: 36, 40, 44, & 48. The other channels it can provide but are not available in Europe are: 149, 153, 157, & 161.

Unfortunately, I don't think so. I believe there are AirPort models produced for different regions in the world. My guess is that this would be something pre-programmed in the base station's firmware and would require a firmware update/hack to do so ... but also be forewarned certain countries prohibit Wi-Fi operation on certain channels in the 5 GHz band as they may interfere with government or military use.

Did I miss something, how is this answered?

As stated "Channels 1-13, 36-64, 100-112, and 132-140 approved for use in Europe"

Well the UK is part of Europe so why are only 1-13 and 36/40/44/48 available on the AEBS?

http://en.wikipedia.org/wiki/Listof_WLANchannels

Yes Wikipedia might be out of date, but Apple's specs show this info too.

I think that the other channels are likely available as well, they are just not user selectable. I believe that those "missing" channels are DFS channels, i.e. channels were the AEBS (and other AP's) have to minimize interference with military radar. The rules of DFS are such that these are not ideal channels for WiFi user experience. I imagine that if you let the device auto-pick the channel then you might find that it picks one of these "missing" channels, perhaps only if the other channel choices are all crowded.

I just received my (NL / EU) Airport Extreme and set it up. I already have an (USA) Airport Express N and an older (NL / EU) Airport Express B/G, so the Extreme actually does the same (except for HD vs Airtunes) as my two Airport Expresses.

The sole reason for getting the Airport Extreme was:
* 3 port Gigabit ethernet switch included
* my Airport Express N is a USA model while the rest of my equipment is NL / EU. This results in a lack of usable channels. Effectively, I could only use channels 1-11 and 36-48. As I wanted to be able to use the full range allowed in the EU I decided to get the EU Airport Extreme and perhaps use my Airport Express to extend the range.

[quote]
+Channels 1-11, 36-48, and 149-165 approved for use in the United States and Canada+
+Channels 1-13, 36-64, 100-112, and 132-140 approved for use in Europe+


As it turns out, I now can only select 1-13 and 36-48 in my Airport Extreme? The sole reason for getting the thing was being able to use the complete range and now I cannot even use the range? I could have sticked with my Airport Express then!

Also, the 'backdoor' using 'command' or 'option' when using pulldown lists does not seem to work either. That did work in the Airport Express N utility...

Anybody got a way to enable to other EU channels? otherwise this is feeling pretty much like a rip off...

[edit]
It seems like the 'option' trick does work for the 'radio mode' pulldown (you get more radio modes available) but still does not work for the channel menu. So it looks like I'm stuck with channels 36, 40, 44 and 48 in the 5Ghz band... I'm thinking of returning the thing cause this is pretty much useless...
[/edit]

As an experiment, set it to automatically pick the channel and see what channel it ends up picking in 5 GHz.

MIne is set to auto and it always picks channel 36.