That is cumulative sales to date, Luis, and that seems about right to me. PIC has been the most popular microcontroller out there for the past 2-3 decades but as you pointed out the tide is turning and Microchip is not coping well with the large and increasingly growing ARM ecosystem of microcontrollers. With the Internet of Things, I bet ARM-based micrcontrollers will dwarf the 7 billion figure within the next decade.
@Max, Regardging your comment, "Cypress Semiconductor has shipped over 1.7 billion units of its PSoC 1 Programmable System-on-Chip... Good grief -- 1.7+ billion units -- I would never have guessed!"
I understand your surprise. It's been a quiet revolution for Cypress in the MCU space, but keep in mind that PSoC1 is the original platform from which CY launched their touch screen controllers and capacitive sense controllers that find their way into all sorts of consumer electronics, control panels, and white goods.
If you mean by "8051-based" all micrcontrollers inspired by the 8051 instruction set and/or code-compatible with the original 8051 Intel device, then yes, perhaps the number is much higher than 7 billion. That said, I do not think this will last for long as 32-bit microcontrollers on modern process technologies are fast, energy-efficient, feature-rich and as cost-effective as 8-bit microcontrollers. 8051 is mainly legacy hardware IMO.
Yes that's true and this will still continue the usage of the evergreen 8-bit CPU based on 8051. Even PIC is simply an other variant of 8051 one can say, as the concept in design is same only RISC and CISC is the difference. Hats-off to 8051/8Bit Arch.