The length of some coaches is around 1:100 or even 1:120. But height should be correct. Width is sometimes reduced to get them through tunnels and over bridges.

Some folks decided to buy only coaches that are 1:87 in length. I am one of those.
Those people are usually called nit pickers, rivet counters, or even uglier names.

Shorter coaches allow people to have e. g. six coaches at a platform that could only hold five full length coaches.

As a modeller, you are king in your own country and you decide what you buy.

Yes Paull, which was why Marklin scales many models shorter than 1/87. Especially in europe, room sizes can often be small.

OO describes models with a scale of 4 mm = 1 foot (1:76) running on HO scale 1:87 (3.5 mm = 1 foot) track (16.5 mm/0.650").[2] This combination came about as early clockwork mechanisms and electric motors were difficult to fit within HO scale models of British trains which are smaller than European and North American counterparts. A quick and cheap solution was to enlarge the scale of the model to 4 mm-to-the-foot but keep the 3.5 mm-to-the-foot gauge track. This also allowed more space to model the external valve gear. The resulting HO track gauge of 16.5 mm represents 4 feet 1.5 inches at 4 mm-to-the-foot scale; this is 7 inches under scale, or approximately 2.33 mm too narro

hess

Yes Dave Märklin are very careful about the running quality of their models.
Track, rolling stock and engines are all made to a standard where they will not foul line-side structures and accessories on a Märklin model layout.
In order to achieve this, Märklin compromise on various measurements.
I also model English OO, and the 16.5mm track is a compromise in itself.
That is model trains for you - compromises everywhere.

Kimball

When I started out as a kid, I was happy with the 24cm tinplate versions of the DSB (danish) coaches.
The even shorter SJ (swedish) coaches went well with them.
I didn´t really KNOW about anything else but Märklin, and wasn´t very much aware of the whole scale thing.
As long as it said "Märklin" on the box, I was happy, as I knew it would work well with my existing stuff.
Some odd Fleischmann, Roco, Liliput and Lima stuff just caused all kinds of problems.
(Electrotren was OK, as it was already made to the Märklin standard!)

As a teenager I was impressed with the 26,4 and 27 cm coaches. I dont think I realized that they were off scale. For a looong time the base of my collection consisted of a "huge" amount of these coaches in era IV.

In the early 2000´s I finally got my first string of 30,3 cm coaches. (A Rheingold era III from Rivarossi/Lima) Finally couplers and wheels were no longer a problem, and I was thrilled.

A few years ago I wanted to go completly era III, so I had to make a choice; Either go the full 1:87 way, or change to Märklins new 1:93 scale.
I chose to stay with Märklin, because of availability and compatibility with my existing stuff.
(At the moment of my choice, Flesichmann still existed as a viable supplier of additional 1:93 stuff, should I need a second supplier)

Today I can see that it would not have been a big problem had I gone the full 1:87 way, and unfortunatly Fleischmann has seized to exist as a H0 brand. On the other hand, I would not have been able to adquire so much new(used) material in such a short time, had I gone the 1:87 way.
Couplers, wheels and interior lighting also seems easier, having stayed with Märklin.