Generally these sites have very clear TOS regarding the use of their feeds. I am not familiar with zdnet's rules, but when in doubt, the best thing to do is ask them as they can easily trace the source of their feeds.
in the case of zdnet [cnetnetworks.com] it seems pretty clear you can't do this without a licensing agreement or at least permission. i'm sure in most cases these are intended for personal usage. you should check the TOS for any site or service before reusing content.