Many people have experienced deaths of someone close to them.
Be it a friend in elementary/high school who had cancer. A family member of old age. Or many other options.
Others have never experienced it.
And then Cory Monteith died.
Sure, Cory was 31 years old, and died of a drug/alcohol overdose, but to many teenagers, this was their first idol, who they had an attachment to, to die.
Yes, many other stars have died at young ages, regardless the cause, but I think this one is the first that affects the American youth as a whole.
Whilst Amy Winehouse was 27, her major fan base in America was people in their 20s. The same for Heath Ledger, and Brittany Murphy, all with slightly older fan bases.
Even Aaliyah, who was 22 at the time she died, didn't have the same impact on teenagers in America.
The fact that this happened when schools were out, may be a blessing, since the next time these kids think about it will be late September, when Glee returns for 3 episodes (the third of which will be a Cory/Finn tribute), before going on an indefinite hiatus.
If they had been in school, they would've talked about it a lot more amongst each other, possibly needing some people on hand, to help them though the "difficult times".
The way I see it, by September, most of them won't remember it as strongly, and when Glee returns, they will help remember him for who he was, and help the teenagers of today, move on with them.