It's a poor analogy that you're making. Read this comment.
By making poor software to sell hardware isn't a really smart move and by having a 4-year old device running well on the latest OS says a lot about the company and its products (software or hardware).
I disagree. I'm an iOS Developer and I know what these devices are capable of.
That's one. Another thing would be that designing software on less performant devices will lead to great performance advantages for more performant ones. Also, who says that designing software for slower devices will impair new or more features for the faster ones? At its core the software must be fast!