...If you're talking about some cut price dead blow like a HF, I'd see your point. Only plastic/rubber I've seen deteriorate on tools was on really old stuff, or cheaper stuff. If you're spending as much as something like a Trusty Cook or Nupla, you're probably not going to have issues.
If something like that is going to deteriorate from sitting in a drawer, it will probably do it within the warranty period. Warranties are generally there to back up the product if a latent manufacturing defect rears its head, not to replace worn out/abused tools.
No, I was actually directly referring to Snap On deadblow hammers made by Trusty Cook (back from when they were the OEM for Snap On, before the hammers were brought in-house). Anyone here who owned one of those orange disasters from the 1990's had it fail on them many years ago. If yours didn't say Snap On on it, you were out of luck when it failed, no matter what you paid for it.
But the problem was in the urethane formulation, and was positively not something you'd discover in a 1 or 2 year warranty period. Still, the clock was ticking on those hammers the day they were made. Last year, I pulled a pair of Diadora bicycle shoes out of the box they sat in for half a dozen years of neglect, and discovered that the soles had the consistency of a chocolate bar in the sun. Melting, weak and brittle, the shoes looked like they were new, except the soles made them trash (and I had to wash my hands in solvent to get the stuff off). This is of course, not an issue you'd ever have with a steel and hickory hammer, but is the reason that I absolutely insist on a long length warranty on a plastic hammer. I understand a manufacturer's reluctance to give out a lifetime warranty. If Trusty Cook stood behind their products with a 25 year warranty (like Leatherman for example), I could get on the bandwagon. And I agree that a warranty shouldn't cover abuse (though wording that as such gives too much power to the person making the decision of what is or is not covered), but a failure in the plastic is a manufacturing defect that absolutely should be covered, and yet isn't, by some big name manufacturers (I could single out TC here, but won't be that harsh).
I've broken a HF deadblow though sheer use (pounding stakes into hard ground where anything else I tried either failed to move the stakes, or damaged them), but I have not had one fail from lack of use. Perhaps time will change my outlook.
