iPhone 4 had and still have its userbase too. Here in Portugal some companies sold iP4 refurbished for 200 euros, few weeks after ios8 launch (yah, ridiculous...).
iPad 1 has the same SoC and RAM like touch 4gen. Market share is bad excuse, since touch 4gen had iOS 6 and iPad 1 did not...
So in September, its time to A5 get discontinued support...
Ss the iPhone 4 did not have 60 percent market share like the iPad 2, iPad 3 and iPad mini 1 have. The iPhone 4 had about 12 percent market share.
Some companies selling refurb iPhone 4's has nothing to do with apple. They discontinued it a year before it lost support ( besides in India). Apple is currently selling not one but two A5 devices in their line up internationally in their stores. You also forget that the iPhone 4 was over 4 years old when it got dropped. The iPad mini 1 and iPod touch 5 (regardless of their internal specs) will only be three years old.
Again the ipad 1 has nothing to do with this. The iPad 1 had a far larger display to power tha the iPod touch 4, and it had a much larger touch interface to run which is far more taxing on the RAM. And again it held a small market share of installed devices.
I repeat, if Apple is intending ios 8 to be a performance fix update, where logically they would be improving performance, then it will be able to run A5 devices.