http://www.macmothership.com/gallery/newads/applebaked.gif Apple has in the past claimed that they will work on smoke damaged machines.
I can understand employees not wanting to touch a yellow or brown mac. I hate working on smokers computers, tar makes a great insulator and does damage components and yet somehow it is your fault that the computer does not work. Neither of the two examples given indicate the amount of tar buildup on the computer, generally if it just smells like a smokers computer, there is no problem, it gets repaired. The only time a computer gets labeled a biohazard is if there is a significant amount of residue on the computer. The first post does sound like tar related damage, which could be considered user abuse(voids warranty).