It baffles me why people don't mention this when the reports on iPad sales are published.
I think iPad sales are actually remarkably good considering that people don't upgrade their tablets as often as they do their smartphones. I think it's safe to say that everyone in their circle of friends and family know one person who is on an iPad 2. These same people likely have an accompanying iPhone which is far newer, such as a 5, 5c, 5s or 6.
The sales have dropped, yes. But they're still remarkably high for a device people treat more like a computer (in terms of upgrade cycles) than a portable device such as a smartphone.
The good news for Apple actually is that they've actually got a significant proportion (40 percent? ) were the iPad is their first iPad - whether first tablet or Android switchers.
The iPad 2 remains the most used iPad even now (it slightly edges out the iPad Mini 1 by about 2 percent). This is impressive for a 4 year old device, and shows that people are obviously keeping iPads for longer - And thats not a problem IMHO - its better for consumers.