Ok I'd like to take a guess here, but I'm really not sure if I'm right!
The coroguard is there on the wings as well (of that I am sure, actually), but it's painted over which requires a special type of (expensive) paint. The main wings are visible for passengers, the stabilizers aren't, which might be why they didn't paint the coroguard sections on them.

Yeah, not sure about that one either: coroguard's been around for eons, and I'm not sure they'd do away with it for that reasons if the beancounters were involved in the decisions.

Hi folks, here's my two-cents worth!
We’ve had a similar discussion before here on the Café. I think this can partly be explained by paint technology. As others have said, coating of wing surfaces helps minimise ice formation caused by cold fuel, provides an anti-slip surface for maintenance as well as protecting against corrosion, abrasion, erosion, etc. My understanding is that advances in paint technology led to development of wing surface coatings using paint rather than the previously familiar corogard. Most airliners now have painted wing surfaces. Corogard type paint only seems to be used on new A320 and A330 family aircraft. A downside I believe is that paint coatings have a shorter lifespan than corogard.
Cheers
Tim

Only the trailing edge and raked wing tip on the 747-8 are made of composite. The main wing structure is metal.

Makes the wings look more modern looking and similar to the 787 and 777 rolling off the production line?

Ken, I pinged a buddy who works there, he says he'll take a look. My latest pet theory is that they left the stabilizer the same, but when they relofted the wing profile, they changed alloys and the new one doesn't corrode as readily.