Wikipedia¹ has a more interesting answer to "Why?" —<p><pre><code> After World War II, the FCC moved FM to the frequencies between 88
and 108 MHz on June 27, 1945. The change in frequency was said to
be for avoiding possible interference problems between stations in
nearby cities and to make "room" for more FM radio channels. However,
the FCC was influenced by RCA chairman David Sarnoff, who had the
covert goal of disrupting the successful FM network that Edwin
Armstrong had established on the old band.
</code></pre>
¹<a href="http://en.wikipedia.org/wiki/FM_broadcasting_in_the_United_States#History_of_FM_radio_in_the_U.S" rel="nofollow">http://en.wikipedia.org/wiki/FM_broadcasting_in_the_United_S...</a>.
I had an Aiwa stereo/receiver several years ago that could tune the FM radio in 50kHz increments instead of 200kHz. Most stations were weaker 50kHz off, but a few were stronger. More interestingly, there were one or two stations I could only get on the even decimals, usually between two empty odds. Now I wonder if someone's transmitter was configured incorrectly, or whether it was an illegal broadcast.
This only happens in the US, probably. The fun fact is that some car manufacturers believe this is global, so they only allow odd frequencies on the car radio.
What actually more interesting to me is that FM has assigned channel numbers. I don't think I've ever seen a consumer radio that used channels instead of the raw frequency. I never knew they existed until I read that.
Yep ... the (unmodulated) carrier frequency is in the middle of the channel (as it is with most AM radio stations). What's more interesting is to look at the old analog television broadcast channels. They were transmitted using VSB AM (Vestigal Side-Band Amplitude Modulation) which effectively meant that the luminance information (brightness) was transmitted using both side-bands (regular AM) but the chrominance information (color) was transmitted using SSB (Single Side-Band).<p><a href="http://en.wikipedia.org/wiki/Single-sideband_modulation#Vestigial_sideband_.28VSB.29" rel="nofollow">http://en.wikipedia.org/wiki/Single-sideband_modulation#Vest...</a>
Never noticed that it's like that here in the US. My radio station growing up was SDR3 on 92.2 and channels are spaced .1MHz apart -- apparently the channel assignment in Germany took a different path.