Well, this probably wont be popular, but I bet a very high percentage of Onkyo failures were user based. Mine was.
Being in the computer business for the last 40 years you would think I would know better, but sadly when I setup my 609 I chose to ignore the manual and only give it about 2" space on top. I had too many components and was simply too lazy to go out and purchase another stand. However I did not join any threads moaning about the poor quality of my receiver. I knew my own stupidity had killed it.
As we all know, heat=death for electronics and my poor 609 lasted over 2 years in that stand, but eventually succumbed.
Currently I have a used 809 on the way, but it will not be abused like the 609 was. It is supposed to run fairly cool anyway from reading the 809 thread. For insurance I'll mount a couple of Noctura's under the top grill to exhaust hot air.
I think some people have had rather poor service from Onkyo as well and have a bit of an axe to grind, thus taking every opportunity to tell you to stay away from Onkyo. Fair enough, but if you read other threads, you find that most brands have some form of problem here or there. Onkyo is known for being pretty accurate in the power spec department and they can run pretty darn hot. Manual said 8" room up top (IIRC) and I wonder if my 609 would have been trouble free if I followed the instructions.
Enjoy your 818, up here in Canada, Amazon.ca wants $1200.00 for an 809 or 818. I found one from a Canadian seller who put less than 100 hours on his year old 809 (never used the amps either, just pre-outs) as it was in a secondary room. I believe him as well. His HT room has 20k of equipment in it.