Where exactly are you obtaining those listed weights? Shipping information from online vendors? If so, you'd be remiss to rely upon that as accurately reflecting the true weight of each rotor. You're barking up a tree where there's no squirrel.

Applying a little bit of analytical thinking would be helpful. You'll note that the examples you posted reflect a difference roughly equal to a doubling of weight for certain examples versus others. So... what are you seeing? A single rotor weight versus a shipping unit of two rotors?

The outlier is the powerstop brand, which is likely: A.) an inaccurate listing, B.) showing the net weight vs. gross shipping weight (although a cardboard box doesn't weigh much), C.) they are lower in mass due to being skimpy (unsafe) garbage - where they use larger cooling vents to save on material costs while maintaining correct external dimensions, or D.) they are lower in mass than the others because they are exotic two-piece rotors, i.e., aluminum hats with steel friction surfaces.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.