Moore’s Law observes that the number of transistors doubles for the same area every two years. Strange that this law has hold for a long time. This has made some people to predict that that 32-bit processors will replace 8-bit processors. The argument starts with the fact that the relative size difference between an 8- and a 32-bit-processor core approaches zero compared with the other resources on the chip as the transistor geometry continues to shrink. When the difference in the silicon area of 8- and 32-bit cores shrinks to nothing, 8-bit processors lose the price advantage that they once enjoyed.
How low can 32 bits processors go? article tells you this and the fact, but also that this is not the whole story. 8-bit controller have their advantages still in applications where their processing power is enough. It is true that 32-bit cores are pushing everywhere (more capabilities and easier to program), but there are still applications where there is good place for 8-bit processors.