I Pay for iTunes Match So Why Does iTunes Radio Now Have Ads (iTunes 12.0.1.26)
I have the same problem, and found something that worked. I skipped around 30 songs, listen to 3 on the same station (as I am writing this post) and no ads.

Devices
iPhone 5s - No commercials there
2 PCs: one with Windows 7 (64-bit) and the other Windows 8.1 (64-bit); 

Problem:
I have iTunes Match and still here ads

Solution:
Enter iTunes → Store → Deauthorize this computer

After
Store → Authorize this computer
Store → Turn on iTunes match