Bob T. Do you know why no 2.4 "off" in AE(ac)?

Question

Actually I was quite surprised by your answer that one cannot disable or turn off the 2.4 GHz radio. 
This surprised me because other non-Apple dual band routers I've had DO offer capability to turn off one or the other or even both, although that would not make much sense.  I mean why buy a dual band wireless router and turn off both bands?
I'd really, really, really like a way to turn OFF 2.4 for several reasons:
1st and foremost, it would cut out one less interfering radio amongst the 11 or so competing around my place. 
2nd, I don't like the idea of that it is out there to potentially be hacked into. 
3rd, would it not save me some energy costs to be able to turn off a radio I am not using?  I mean Apple touts all their "green" initiatives and "earth friendly" processes!  Saving some enrgy seems in line with that propaganda, yes?
4th, as I said above, it is a feature on competing products.
5th, I'm pretty sure I could come up with yet another reason
Do you know maybe if it was some sort of technical design decison?  Or maybe the engineers did not think about it as a great feature for all the reasons cited above?
I wonder if this missing function could be fixed with a future firmware update?
I have exclusivly named my 5G network and ALL my devices happily connect to that network.  Fantastic througput as I am the only dude currently on that freq. So really no need to consume precious enrgy operating a radio I don't use!  Yes?
Sometimes Apple shows such brilliance and other times, one wonders, what were they thinking (or not)!  For instance, it was a resaoned decision NOT to include a CD/DVD disc device in the latest and greatest iMacs.  You think there was some sort of reasoned decision to NOT provide a radio off switch?

Answer 1

On my single-band TimeCapsule 1st generation and on my Airport Express 802.11n (1st gen), both using firmware v.7.6.4), I can specify:
802.11n only (5GHz)
802.11n only (2.4GHz)
That is quite true for the non-simultaneous dual-band AirPorts. You can configure them to operate on one or the other band ... effectively disabling one or the other radio.
The reason the early TC and AE are single band is that they have only one wireless.. but it is dual band.
You are not disabling one radio or the other .. you are setting the one radio to use 2.4ghz or 5ghz. This was very common when the cost of the wireless chipsets was high.. as the prices came down and the cards were made more compact.. so they could fit two full separate wireless devices on the one card.. and they can then be properly tuned to 2.4ghz and 5ghz instead of needing to cover both bands.
Pictorial history.
Gen1 & Gen 2 AE. Gen1 TC. You can clearly see the amplifer chips for each channel but only one control chip.
So it has 3 antennas. I am not 100% sure of the layout.. as I look at the board I suspect it has a single 2.4ghz and single 5ghz with a dual band antenna in the middle. Based on Atheros.
Gen 3 AE.. Gen2 TC Dual band simultaneous.. 4 antennas.. dual stream. So each band has only 2 antennas.
Gen 4 AE Gen3 TC  Changed to Maxell wireless.. and clearly see there are 3 amplifier chips.. This is 3 stream on 2.4 and 5ghz.. simultaneous. Each band shares the middle antennas.. ie there is one 2.4ghz only antenna, one 5ghz antenna.. and a pair of dual band antennas in the middle. So from 4 antennas they effectively have 6. changed the port type to faster port. I guess the earlier ones are mini-PCI and with the revised board changed to mini-pci express.
Gen 5 AE Gen4 TC.. obviously changed to broadcom.. 
Same arrangement.. clearly see the amplifier chips.. 3 for each channel.. and same antennas.. 6 by sharing the middle two as dual band.
Taken from info in smallnetbuilder.. for each model AE.
Gen 6 AE and Gen 5 TC you can see from http://www.ifixit.com/Device/AirPort_Extreme_A1521
AC is very different beastie.
6 antennas with AC wireless. The colour circles are added..
From ifixit article.