The theory was well illuminated by others. The nuts and bolts (or the bits) in this case are:

> perl -le "print unpack q/b*/, pack F, 36.8"
0110011001100110011001100110011001100110011001100100001000000010

> perl -le "print unpack q/b*/, pack F, 36.6+.2"
1110011001100110011001100110011001100110011001100100001000000010
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As you can see, there is a bit of difference. The lowest-order bit, to be exact.

FYI: This, of course, is on Win32. On other platforms it may be different, both in encoding and the round-off error in the last bit.