You assume there is a widespread problem that Apple needs to "address and resolve," beyond honoring the one-year warranty as individual cases arise.
Apple sells Macs currently at a rate of over 12 million per year. By now, if a million new iMacs have been sold, even if only 1 in 1000 customers have a hardware problem, that's 1000 customers with hardware problems. I don't know what the actual problem rate is with the new iMacs, but reading a few dozen or even a few hundred problem reports does not indicate there is a general problem. When you sell a lot of something, even if only 0.1% are affected with a problem, it will be large number of customers; conversely, it means the vast majority of customers have no problems because Apple's customer support systems (and Apple Discussions) are not being overwhelmed.
And if you happen to be affected by a hardware problem, that's the purpose of the one-year warranty and optional AppleCare.
Also, while Apple Discussions is a great way for individuals to get their individual questions answered with the help of other users, it is not a verifiable, consistent, nor comprehensive source of quality control data. For every problem report you read, you have no idea if there are 10, 100, or 1000 customer with no problems. People with no problems generally will not bother logging onto Apple Discussions (or any other forum) just to post that they are having no problems.
For your question about web designers and developers, using a new 27" iMac for this purpose would not be any different than using any recent Mac (except maybe having a larger screen to work with). You should look for forums, articles, and reviews related to whatever development tools you happen to use for your work. You should also mention what those tools happen to be here, so that users who also use the same tools can comment. If those current tools happen to be Windows only, you should stil mention what they are.