score:4
This appears to be a simple "translation" issue.
If you look at these two products on the US Amazon site, both are shown as a "30 inch" model, and both have their external dimensions listed as "17.5 x 12.9 x 30.9 Inches".
"17.5 x 12.9 x 30.9 Inches" converted to centimeters is "44.5 x 32.8 x 78.5" which matches exactly the size shown on the pages you've linked to (with the 32.8 rounded to 33 which is only a difference of 2mm).
Thus it seems most likely that when translating this products page from English to German they simply incorrectly entered the size of the "74cm" model, and it should actually be stated as "78cm" as per the second suitcase. One way or another, both bags are the same size (and based on the photos, appear to be exactly the same bag only in a different fabric!)