fatter skis have more material, which typically weighs more, and thus, may be harder to spin. i wouldn't say it's much harder, but it's different. also, wind resistance does have something to do with spinning, but it's not noticible.
anthems are so light and the swing weight is so minimal it isnt even a factor. they are lighter than many skinnier sandwich construction sksi I have felt.
Yeah it just depends on the skis, honestly. Anthems are a park ski, and 10 mm more isnt a big deal. I had Bacons and tried to spin those and had a significantly harder time spinning because they were so heavy. After you get past about 95 mm, then you have to ratchet down the tricks from like a 5 to a 3, or a 7 to a 5, etc.