Too Many Different Parts!

It's been dead in the shop, so not much has been happening or has been worth mentioning, except an issue a customer had with a starter off a 2002 Mercedes CLK.  He ordered a starter off the Internet and then brought the vehicle to the mechanics shop, that's across the street from my shop, to swap out the starter.  They had trouble installing the new starter because it was about an inch longer than the old one and would not go into place! 

So the customer brought the old starter to my shop to see if I could fix it right then!  Because of the thousands and thousands of different parts that don't interchange I didn't have or wouldn't even stock the part I needed to repair his starter.  Then they brought me the new starter to see if I could change the parts needed over to the old starter, but as it turned out the new starter was also larger in diameter than the old starter and the parts wouldn't interchange.  With the customer's permission, the mechanic ground out some metal in the frame or something, so he could get the longer starter into position.

Checking the computer I found that Mercedes used two different models of starter for that vehicle and engine size.  Why?  Why in the hell did they do that?  Who's the SOB who thought up using more than one starter?  Why didn't they just produce one starter for the vehicle or for a large number of their vehicles!  This practice, used by all the manufacturers, has caused a large number of headaches for a lot of people and wasted my time, my customer's time and the mechanics time dealing with this issue.  Maybe if the auto manufacturers had to pay us for all the lost time dealing with issues like this, they would change the way they built cars and made them simpler and more interchangeable!