This is true, but it is also still true that identical chargers are included with every single device. Even if you only have one tablet and one mobile phone in the whole household, you still have at least one charger you won't use, because the odds that you'll have to charge both the tablet and the phone at the same time are not particularly high. Why even use the charger when you can just plug the USB cable into your computer and charge the device that way? It's slower, but the device is right next to you, and you're usually at the computer for a long enough time to sufficiently (if not fully) charge the phone/tablet.

An additional problem is that you don't need more chargers because they break too often, but that you need a good charger which won't break anytime soon. Good chargers won't be included even with the most expensive devices (just look at the junk Apple's devices come with, which is generally already broken in the first week), and why would you want to contribute to the pile of technological waste by buying cheapo chargers (as part of the device package) rather than just buying one or two good ones which will last a very long time?

It's the same thing with tin can earphones or any other rubbish manufacturers put in the boxes of their products, they're of such low quality (both in material and in the sound they produce) that no one in their right mind would use them. Better to buy a decent pair of earphones separately which will last much longer and sound like heaven compared to the ear-piercing shrills of the earphones packed in the box of your phone.