iPad 1 got 3, 4 and 5.
iPod touch 4G got 4, 5, 6.
iPhone 4 got 4, 5, 6, 7.
... this is exactly what I said, except you also added the iPod touch. Not sure what you're implying. If you're pointing out the difference in their longevity let me point you to how I mentioned the RAM. The A4 on each device had different tasks. The iPad had the highest resolution and 256mb of RAM. The iPod Touch had the same RAM but a lower resolution than the iPad to deal with. The iPhone had double the Ram of both devices but the lower resolution of the iPod compared to the iPad. Which is why you get the full 4 years of life out of the iPhone.
Next year? They're still selling iPad minis with A5s in them. No way does support for those get retired so fast.
So? They sell the 4S this year, and sold the 4 last year. Then when iOS 7 and the 5S came out the 4 got cut and it's last update. The 4s will see the same happen this year with 8 and the 6. They won't continue selling the device, and it won't get iOS9.
The mini won't either, the software won't support it, and they will discontinue it as they did with the iPad 2. That would give the Mini 3 years of support, same as the first iPad and it came out a year late as far as hardware is concerned so it makes sense that it wouldn't get 4.
Not sure why you would think any different, it's the exact pattern that has happened for the previous devices, there is nothing unique about it to think any different. The A5 while great is not 64bit, and has 512mb of RAM. When every device being sold by end of year is A6+ as well as 1GB RAM + next year when we are looking at the A9 and 2 models with 2GB of RAM and the weakest device having a 64bit A7 with 1GB of RAM why in the world would they continue to support the A5. You can bookmark this one, I'll take whatever dumb avatar you want to give me for length of iOS 9 if it is supported on iPhone 4s or iPad mini/iPad 2.
Devices 2010
iPhone 4 - A4 512mb - iOS 4
iPhone 3GS iOS 3-4
iPod Touch 4G - A4 256mb - iOS 4
iPad OG - A4 256mb - iOS 3
2011
iPhone 4s - A5 512mb - iOS 5
iPhone 4 - A4 512mb - iOS 4
iPhone 3GS iOS 3-4
iPod Touch 4G - A4 256mb - iOS 4-5
iPad 2 - A5 512mb - iOS 5
(Discontinued) iPad OG - A4 256mb - iOS 3-5(Max at iOS 5)
2012
iPhone 5 - A6 1GB - iOS 6
iPhone 4s - A5 512mb - iOS 5-6
iPhone 4 - A4 512mb - iOS 4-6
(Discontinued) Phone 3GS iOS 3-6(Max iOS 6)
iPod Touch 5G - A5 512mb - iOS iOS 6
(Discontinued)iPod Touch 5G - A4 256mb - iOS 4-6(Max of iOS 6)
iPad 4 A6 - 1GB - iOS 6
iPad 3(lol okay) - A5x - 512mb - iOS 5-6
iPad 2 - A5 512mb - iOS 5
iPad Mini - A5 512mb - iOS 6
2013
iPhone 5s - A7 64bit 1GB - iOS 7
iPhone 5 - A6 1GB - iOS 6-7
iPhone 4s - A5 512mb - iOS 5-7
(Discontinued) iPhone 4 - A4 512mb - iOS 4-7(Max iOS7)
iPod Touch 5G - A5 512mb - iOS iOS 6-7
iPad Air - A7 - 1GB - iOS 6-7
iPad 4 A6 - 1GB - iOS 6-7
(Discontinued)iPad 3(lol okay) - A5x - 512mb - iOS 5-7
(Discontinued)iPad 2 - A5 512mb - iOS 5-7
iPad Mini Retina - A7 1GB - iOS 7
iPad Mini - A5 512mb - iOS 6-7
So there's a pretty obvious pattern of 3-4 years of support, as well as having only the prior two generations of devices being sold. The year the device becomes the 3rd generation from current it stops being sold and receives its last OS update that year. So this year should look like the following.
2014
iPhone 6 - A8 2GB - iOS 8
iPhone 5s - A7 64bit 1GB - iOS 8
iPhone 5/5c - A6 1GB - iOS 6-8
(RIP) iPhone 4s - A5 512mb - iOS 5-8(Max Final Update iOS 8)
iPod Touch 6Gb - A7 1GB - iOS 8
iPod Touch 5G - A5 512mb - iOS iOS 6-8 (Max Final Update iOS 8)
iPad Air 2 - A8 2GB - iOS 8
iPad Air - A7 1GB - iOS 7-8
(Discontinued?)iPad 4 A6 - 1GB - iOS 6-8
(Discontinued)iPad 3(lol okay) - A5x - 512mb - iOS 5-8
(RIP)iPad 2 - A5 512mb - iOS 5-8 (Max Final Update iOS 8)
iPad Mini Retina 2 - A8 2GB - iOS 8
iPad Mini Retina - A7 1GB - iOS 7-8
(RIP)iPad Mini - A5 512mb - iOS 6-8 (Max Final Update iOS 8)