My theory on the carseats (keep in mind this is a theory, I could be talking out of my backside) also has a lot to do with how they are used. You leave them in the car which in some areas can have some very extreme temperature differences. Think about the warnings of leaving pets or children in hot cars. Your carseat can become baked on a regular basis over the summer, a hot car in the sun in a hot climate can get up to 120-140 degrees. This will bake and soften the plastics. On the other extreme, in cold climates, the plastic can freeze and this will could cause it to become brittle. I think (like I said, not proven) that the 7 year window is based on the guarentee that the plastic will hold up under extreme conditions. We're likely to replace our carseats that our in the garage we purchased new when my 8 (almost 9) year old was a baby.
On that theory, I'm a little less worried about toys and non-safety items. We have hand-me down toys that are plastic and well over 10 years old. For items that a baby might put in their mouth, we toss, but the non-chewed on toys (like the play kitchen I took to the goodwill in June) we plan to reuse. It's a personal opinion. :)
Honestly, if you don't think a toy is safe, don't keep it. Toys have a way of multiplying on a pretty regular basis, so there will be toys. I swear I let one barbie doll into the house against my wishes and that doll somehow managed to multiply into a bin that we can't put a lid on. I have NEVER bought a barbie doll (kind of hate what they teach little girls).