Question:
I checked out the Insterstate Distributor Company web page (I know that a newbie wouldn't get hired there but I was curious) and it had a breakdown of the LARGE difference between splitting mileage versus splitting mileage pay. I'm posting it below, but just go to the company's web site and look up the compensation if it gets taken off of this site for copyright reasons (didn't appear to be an issue with me).
I don't work for IDC or any other truck company (I'm a maybe wannabie), but I find this to be quite enlightening:
We have a great team pay package! Our premium starting mileage pay is further enhanced because the total miles driven are not split between the two drivers. The following example shows how that puts more money in your pocket with every paycheck.
John and Mary Smith run 21,000 miles a month at Interstate Distributor Co. They each had one year OTR experience, so their mileage pay is $.42 split but their miles are not split.
John: $.21 x 21,000 = $4,410.00
Mary: $.21 x 21,000 = $4,410.00
TOTAL = $8,820.00
Cecil and Sally Jones run 21,000 miles a month at XYZ Trucking. They each make $.30 a mile ($.60 for the team) however their company splits the miles ran between the two of them. Here's what they would make:
Cecil: $.30 x 10,500 = $3,150.00
Sally: $.30 x 10,500 = $3,150.00
TOTAL = $6,300.00
NET DIFFERENCE = $2,520.00
"I'd rather have a bottle in front of me than a frontal lobotomy."

Answer:
Pay teams like that. The team will earn X per mile (say 40 cpm) for all dispatched miles. Each driver then recieves 1/2 of the pay.
I will always be a mutter trucker at heart.
Answer:
In your second example, the company is NOT paying $.60/ mile. It is paying $.30/mile. This accounts for the difference. If companies are really doing this, they are taking advantage of those truckers who are operating on only a 3rd grade education.
MrClark
"What, me worry?" -A.E.N.—Groucho Marx 1890-1977