Selectivend vs sure-vend

Howdy all,
I've been killing time reading about machines in Jeff's book but have yet to find out why two practically identical machines were made by two different companies.  To me, the Selectivend S48 (Dr Pepper) and Surevend S47 (Pepsi and 7up) are really more or less identical. Same goes for the 96 (Selectivend - Dr Pepper) and the 95 (Sure-vend - Pepsi).  The machines could pass as twins except for the bottle count which is off by one bottle (why?) and slight differences in the coin door.  Anyone know more about these differences?  Were Selectivend and Sure-Vend the same animal like the difference between a chevy or GMC truck?  Thanks in advance for satisfying my curiosity.  
A J