I have to say the problem with the AC adapters is mostly user error.
I've never had an AC adapter fail, so I'm not sure where you get your "a lot of people" figure from.
Fraying, burning, etc.; I see many folks like to wind their cords tightly instead of leaving some slack. This what I call user error.
Yeah, who really will intentionally log in, write some glowing review for a damn AC adapter? Also 1500 reviewers is very few people.
EXACTLY.
When is the last time you got to work and said "Gee, there was a red sedan that was courteous, used their turn signal, and followed the speed limit?". Okay, now, when was the last time you got to work and said "Some idiot cut me off in traffic!"
People are much much more likely to complain about something poor than to write a good review, save for a more substantial product. I can't even imagine writing a review for a Magsafe adapter, I would've never thought to do that. I might, if I felt like doing such a thing, write a review for my iPhone or my MBP though, which I've been relatively pleased with.
Most 'common problems' are isolated to a few hundred or even thousand people among millions and millions. However, internet forums/reviews/etc. will be saturated disproportionately because those who experience the issue are many many times more likely to post about it, than those who don't. Think about MacRumors, the vast, vast majority of users are either asking a question regarding how to use their machine, or reporting a problem. Few get on just to say "Hey it worked fine today, didn't have any issues". That, of course, doesn't include the dozens of threads every day about the Retina Macbook Pro vs Classic, whether they should wait for haswell, or when the next upgrade is going to be by search and/or scroll down challenged posters.
Also, much of the fraying can be prevented by taking care of your product! It's easy to get the cable bound up and bent, don't let it. For example, when it sits on my night stand on the charger, the cord first goes around my lamp, then to the MBP, so that it doesn't fall down and 'crimp' at the connector, which can stress it over time.
You'll find, with MagSafe adapters, that people either have no problems with them, or have repeated problems, suggesting it's not the adapters fault (poor electricity supply is probably the number one culprit).
I keep mine plugged into a surge protector, and don't abuse the cable. And guess what, in ~7 years of owning MacBooks with a MagSafe adapter, I've never had one fail.
Another +1. They are frayed due to poor handling and just being thrown around. If they are failing but not fraying, those individuals ought to think about whether or not light bulbs don't seem to last very long and/or other electronics seem to give them issues, as they may have fluctuating voltage or over-voltage in their home, something they should consult an electrician about. A slight over-voltage in their home will cause accelerated wear, but not necessarily instant destruction of components, which is why it often goes undiagnosed (they blame the product, not their home).