The Model A was upgraded as the improved A+ (more GPIO pins and lower power consumption), albeit with a gap in availability of the A until the A+ could be produced. However, that was in response to slow(ing?) A sales and increasing huge demand for other models, IIRC. If one is accustomed to typical industrial controller unit prices, buying enough Pi 2B boards for the lifetime of the project, and then some, should be a no-brainer, given its incredible value for the price.
You need to understand that the availability of Pii for the industrial market is a very happy side-effect of an effort to provide a low-cost device to the education market. Even that turned out to be a delightful artifact that grew out of an initial intention to only produce enough for a single university's computer science recruitment pool numbering in the low thousands over a period of at least five years, IIRC.
Think of the Pii as light bulbs, i.e., commodity units at commodity prices, although very, very bright (in the intellectual sense) light bulbs
The best things in life aren't things ... but, a Pi comes pretty darned close!
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!