[s-cars] That old dead horse, oil

[John Farr]

I know opinions differ, but I've always had good luck with Mobil 1.  
My question is what is the difference in the "new" formulas, gold top  
'extended' vs red top 'performance driving formula' 15W-50, or,  
silver top "new" 0W-40 vs black top 'european car formula'.
In the 0W-40, which I use in the '02 S6, the black top is "SL/CF  
energy conserving". The silver top is "SM, SL/CF". The black top  
meets VW 502.00, which opens another can of worms. A of A says this  
is required, but the stealer uses some cheap blend for their "free"  
oil changes. I gave up and just bring my own. The silver top doesn't  
say that it meets that standard. Go figure!
Is this just a marketing/packaging ploy, or should I be concerned  
that I'm putting a lesser product in my beloved Audis? I'm convinced  
that the reason I have 217,000 miles on the S4 without using a drop  
between changes is frequent swaps with the best oil.
John
'02 S6
'93 S4 (semi-retired but going to school this weekend!)