Question about Russian/Soviet vehicles

[mr_clark]

I am just playing a Russia vs China game in 2008 and I have come about the following problem:
I had purchased a platoon of Spetsnaz to go with my assault force and now planned to buy transport for them. I was (a little) astonished to find out that the Spetsnaz squads couldn't be transported the whole BMD series and the modern light APCs as the GAZ-3937. Evidently it's because the vehicles have only a carry capacity of 106 opposite to the 109 of the BTRs and the BMPs.

My question now is whether this is intentionally so and why, especially the BMP/BMD which had been designed for the same amount of troops to be transported, this difference is given.
(My magazine states that:"Der BMD trägt neben seiner Hauptbewaffnung auch einen Luftlandezug, der im Innenraum wie beim BMP platziert ist." English:"The BMD carries next to it's main armament also an airborne squad, that is seated like in the BMP")
As far as the old GDR military-magazines I have state the BMP to carry 7+crew while the BTR carries 8+crew, I can't really understand the distinction made between BMP and BMD and none between BMP and BTR.
Additionally globalsecurtiy.org states that "The seating capacity of GAZ-3937 is 10 people." with a crew of 2 or even just a driver as in the game (1 man crew) that leaves at least the same room for troops as the BMP, it will most likely surpass it.