Histogram and bin sizes

I've always wondered why you have to use a constant bin size with
HISTOGRAM().  To quote J.D.'s famous tutorial:  "a histogram
represents nothing more than a fancy way to count."  Doesn't an
imposed constant bin size imply that this is the only way it's ok to
count?  I can think of several reasons i wouldn't want to do this - I
used logarithmic bin sizes in my dissertation, for example (now i'm
hoping someone isn't going to answer this post saying i screwed up in
my dissertation :-) ).  And besides, Excel lets you use arbitrary bin
sizes....and if Excel lets you do it, it has to be ok, right???? ;-)

Jeff