Langstroth Hoffmann frames (standard) have a width such that the center of
each comb is 1 3/8" away from the center of the next.  When the comb is
built out from foundation you're left with your bee space between the comb
surfaces. When Chas. Dadant came up with his hive design he incorporated
brood frame widths of 1 1/2" instead of 1 3/8".  The Dadants claimed that
the ventilation was better with the wider spacing, and that the bees
wintered better.  (In nature the combs can be found that far apart.)
 
I agree that after a year or two it gets hard to deal with a full
complement of 10 frames in a hive body.  The propolis gradually builds up
and gets in the way.  I used to scrape down the edges of the frames to get
rid of it but that is a pain.  I even got some "frame grips" to get that
first comb out, but that didn't solve the problem, either.
 
Following the advice of Walter Kelly and Richard Taylor  (and much of the
commercial crowd) I finally went to 9 frames, and I've found that the work
is much easier now.  (Many of my frames are old, and with 10 of them
cemented into a brood box I would often have them break when I tried to
separate them.)  With the 1 1/2" spacing, leaving just a very slight space
between adjoining end bars, the frames are easier to remove.  Follower
boards to take up the extra space would be fine but another piece of
equipment to worry about.  Instead, I just let them build the two outside
combs out a little thicker, which they will, since there's a bit of extra
space at each end.  This is no big deal, cuz those combs are only going to
have food stores in them anyway. (keep the best combs in toward the center
for the queen, lousy ones at edges).  It's easy to get one of those end
frames out, leaving you lots of working space.  On the other hand, if you
just haphazardly leave 9 frames instead of 10 without spacing them, some
brood combs will be thicker than others or crooked and that can be a mess.
After a while the propolis between the frames makes an automatic "spacer,"
to some extent.
 
With two (+) deep boxes for brood the queen has plenty of space on 18
frames.  It would be an exceptional queen who could even completely lay out
9 frames.  & in single brood chamber hives I have seen the queen lay right
out to the hive walls on both sides, without follower boards.
 
I've tried tunnel entrances (an insert that is sort of like the front
section of a Killion rack).  Made em from tempered hardboard.  It did cut
down on the gnawing of the bottom combs, but eventually the bees really
chewed the boards up so I guess they didn't like them.  And, again, it's
another piece of gear to contend with.  What's nice about the Miller -
Killion floor design is that you can slide a comb of honey in there
sideways for feeding, after you remove the rack part.
 
(In Germany many beekeepers using standard Zander frames also prefer 9
instead of 10 in brood chambers, and the Scottish Smith hive is often run
with 1 1/2" wide brood frames too).  If you're really cramming the bees to
get them to work the section boxes, then do as Dr. Miller and the Killions
did with racks and followers.  I'd rather keep it simple and put those
resources into super space for the crop.  With appropriate supering there
doesn't seem to be excessive burr comb with 9 fr.  Well, there's always a
colony or two...