IMac failures

Question

I have tried unsuccessfully to find an email address for Apple, where I can give critical feedback about my iMac experience and expect to have some response.  The only feedback channels make it clear there will be no response and I fear it disappears into a black hole.  So I'm posting this here in the hope that someone might offer a contact e-mail or reflect on my experience.
I bought a 21.5" iMac in 2010.  Just after the end of the Applecare agreement, the DVD drive failed and had to be replaced at my expense.  Last year the screen went blank, other than grey pixellated stripes and the faint log-in icon.  Assessment by our local computer repair shop (not an official Apple retailer/repairer, but experienced in dealing with Apple issues) suggested that the graphics card (Nvidia G-force, I think) had failed, probably with the solder connections having melted as this was a problem that had been a common issue with my model/age of Mac.  Indeed, they thought that Apple had repaired this fault free within a certain period of purchase.  They suggested the most economical way of repairing this was a specialist in London, with a three month guarantee.  I took this option and 3 months and 2 weeks after the return, the same fault occurred again.
I decided enough was enough and have bought a new iMac....albeit with some annoyance and without total confidence. 
Am I just unlucky?  Am I unreasonable to think this level of component failure is unacceptable?  Apple charges a significant premium for its products (its record profits recently announced are unsurprising).  Given the quality of build and design that they presumably regard as justifying this, is a 4.5 year lifespan for an iMac the norm?  My use is purely domestic and way below the use that many Macs must experience.

Answer 1

Stamfordian
Yes Apple had a succession of badly designed iMacs. The white 24" iMacs were a particular problem. I had two fail with identical problems.
I also had problems with the first 24" Aluminium iMac with failed network card and power board. I insisted Apple replace it after the second repair still did not fix it.
The hard drive failed in my 27" iMac 30 days after I bought it. I was particularly upset because when I researched it, it was a known problem, but Apple did not warn me and I lost a fair amount of work.
In my long experience Macs suffer from design failures due to Apple trying to slim down the design too much, causing overheating, or because of some other unusual and unconventional technology which proves more experimental than practical. Some of their components, at least the cases, are better built and better material but otherwise Macs are not any more reliable than modern PCs which if bought from major suppliers are very durable.
Apple works hard at the myth of superiority to justify their higher prices, it is hard to get them to even talk about problems, they will just go silent unless it flares up into a major media story.
As compensation the service and support from AppleStores is good and the unified hardware/software leads to less finger pointing when you have a problem, Apple has to own the problem and fix it if it is under warranty. I have had entire units replaced if I made a clear case for it, without too much fuss.
Peter