I have never seen any testing of a 5 yr or older helmet proving that it doesn't provide protection anymore.
So all I conclude at this time is that they want to sell helmets.
styrofoam is listed as degrading in 1+ million yrs. The problem is that the numbers never suggest the mechanism of decomposition. There are several - heat, biochemical, mechanical, irradiation. In the case of styrofoam, that material is biologically inert (microorganisms have a hard time eating it) so a long decomposition time is expected. However it is subject to degradation when exposed to sunlight (UV radiation), thermal energy (the bonds break when it gets hot enough), mechanical degradation (it erodes and wears away) and chemical attack (it burns). Under these conditions the decomposition time is much shorter.
1981 CB900C, 1998 GL1500C Valkyrie
"Our Constitution was made only for a Moral and Religious people. It is wholly inadequate to the goverment of any other."
John Adams 10/11/1798
"If we ever forget that we're one nation under God, then we will be a nation gone under" Ronald Reagan