The Revos on my Titan did that. I didn't run them to the end because I sold the truck. The Michelin CT's that came on my T4R have the same thing but a lesser degree. The Toyo's on my girlfriends car have it, the Yoks on the 1500 Dodge have it, the LTX M/S on the dually F350 have it...
I'd say if there's no significant depth or separation I would not worry about it...
Our road temps exceed yours, our speeds are probably higher. I-75 between Ft Myers and Sarasota is 90mph for a long duration. I think the heat puts minor surface fractures in the most outer layer of rubber. I also speculate the heat is why it's a 'normal' condition to my eye and you're not as accustomed to it.
:cheers: