i've seen all of that service life info too. those numbers are just when the airframe is estimated to last. obviously the f-117's are not being retired because their airframes are not airworthy. an aircraft can be retired before it's "service life" expires. the article i read was probably inaccurate... but it simply said that there was no justification for spending the billions of dollars on the b-2 when there wasn't a need, and that it was planned to be put in davis montham's boneyard. may not be true...
I don't think it would be viable to put the B-2's in the boneyard anyways. From what I read they need to be stored in hangars to protect their radar absorbing skin.