One factor that is always a concern in the production of professional art and craft materials is whether they are "archival" or not. That is, will they remain stable over time and not deteriorate over a period of years, decades, or even centuries. Obviously this has never been a concern in the scale model arena (serious ship modeling may be the exception), especially with regard to the tire issue, as well as decals, some paints, metal foil, etc. Anyone who collects acetate promos or even-more unstable WW2 identification model planes recognizes that this type of plastic was not meant to stand the test of time. Luckily, styrene does seem to hold up reasonably well in spite of its tendency to discolor (whites turn yellow, etc). If you've got model cars that are 30, 40, 50 years or even older you'll recognize this issue. Does it concern you?