You should not discount the posted dimensions of the trolley you are considering.
Outside dimensions are important, as the Cabin "M" and "L" are actually in excess of what most carriers declare as their maximum allowable dimensions.
Interior dimensions are important, because, like "1Bag1World" mentioned, interior design dictates available packing space.
I own the 32L RIMOWA IATA Topas Titanium and 32L Topas (Model 920.52, two-wheel trolley).
I prefer my two-wheel 32L Topas, as the interior compartment opens in a 1/3-2/3 split compartment.
The four-wheel Cabin trollies open on a 50/50 split compartment.
That small difference, allows me to pack clothes, compressed, in the 1/3 section of the compartment, while I can fit larger items into the deep 2/3 section of the compartment.
Volume is accurate, but not necessarily a true reflection of its packing capabilities.