Never be put off any purchase from what you read on forums as a rule of thumb.
If there's a widespread issue that's affecting all devices, then every single owner will complain about it and in all likelihood there would be a product recall or a fix in the works.
Beyond that, you are always going to see a disproportionate amount of complaints on forums and so on.
It's human nature, when there's a problem we complain about it. When everything is hunky dory, we don't.
So the unfortunate people who have an issue with any product are going to be significantly more vocal than those who don't. And yes there are, with absolute certainty, iPhones/iPads and every other product that have problems.
When you manufacture any product there is a failure rate. It's unavoidable, nobody can mass produce anything with a 100% perfect rate. That's fine, it's expected and we all know it.
The trouble is when you mass produce a product in volumes such as Apple do with iPhone, which ultimately ends up being over 100,000,000 devices. Even a failure rate as ridiculously low as 1% would still mean that there's 1 million faulty devices for every one hundred million manufactured.
That's a whole hell of a lot of devices and unhappy customers. Which means there's going to be a huge amount of complaints on forums and social media and press who like to blow things out of proportion.
We're very fortunate though that Apple has the best customer support in the world. If you're one of the unlucky few who experiences an issue, they'll replace your device. Usually on the spot if you go into a store.
Beyond that they even have a brilliant no questions asked 14 day return period. And their after-sales service, often even beyond the warranty period (which I've experienced myself,) is nothing short of spectacular.
So really, don't worry. Buy the product you want, there's significantly more probability that you won't have a problem. And if you do, you can return or exchange it with no quibbles.