Here is a link to what I would personally call a "major manufacturer" Shoei.
http://www.shoei-helmets.com/Maintenance.aspx
What it says is this:
Helmet Replacement
Ultimately, the useful service life of a safety helmet is dependent on the intensity and frequency of its use. Helmet replacement is recommended even if only one of the under-mentioned points applies:
1.The helmet was subjected to an impact.
2.The comfort padding or the retention system has become loose due to heavy use or display signs of deterioration.
3.The synthetic foam padding displays signs of heavy use and the helmet feels too loose. Test: with the retention system fastened, the helmet turns to the side when you gently shake your head.
4.There are indentations in the EPS liner and/or white scratches can be seen on surfaces with black paint.
5.Even if none of these is applied, we, SHOEI, recommend replacement in 5 years after it's first purchased at retail.
My understanding is that #5 means exactly what it says. It doesn't say that helmets will disintegrate on the shelf in the store after five years, and become "deemed unsafe". I'm going to also asssume this is why you see older model helmets still for sale on the shelf at a lot of stores.
To the OP. Don't believe everything you hear. Do the research yourself. Contact AGV. The info I posted is from Shoei but my guess is they will say something very similar. But what do I know, it's only some crap Shoei posted on their website. I'm sure they could have been drunk when they wrote that

rolleyes