You can't have been looking very hard, then.
And IAP purchases being hacked is rather irrelevant - anything can be hacked. The fact is that piracy of paid apps on Android is incredibly easy, to the point where apps that would do fine on other platforms struggle to make back their development costs on Android. It is a harder to hack IAP than circumventing the poor DRM system that Google offers its Android developers. Combine this with the fact that games with IAP also do a lot better on all mobile markets than paid apps, means that IAP will become increasingly dominant.
That aside, there is a difference between using IAP as an upgrade option (instead of having a free and a paid version of an app) and using IAP to sell limited-use game "objects". IMO, to not distinguish between those two cases is doing both yourself and developers a disservice.
This is incorrect. Or to put it more precisely, "it depends".
There exist three types of in-app products on Android: "managed", "unmanaged", and "subscriptions".
Managed in-app purchases
always follow your account. These are one-time purchases per Google account. If you've purchased them once, you can not purchase them again using the same account. Change phone, uninstall/install, etc... the purchase will remain. IAP to remove ads or add DLC will usually be of this kind, unless the app developer is trying to rip off his users.
Unmanaged in-app purchases is what you guys are all discussing. Any IAP that can be purchased more than once will be unmanaged. Unmanaged purchases will tend to follow the app only, unless the developer stores the purchase information on his own servers.
Subscriptions are exactly what they sound like. Recurring, time-limited in-app purchases. Subscriptions automatically follow your account, and can be cancelled at any time.
Or to put it briefly: IAP is not an inherently evil or exploitative system. What developers do with them, might be.