Uhh, I've never seen a Microchip ad before. I believe Atmel spends a lot more money advertising. They give deals to universities and put ads in the Mouser catalogs. PIC micros pack a lot of peripherals on their devices. Atmel does, also, with the AVR devices but PIC was doing it first. So there are more tutorials and books for PIC. Historically, Microchip has been very friendly to hobbyists. Until recently, you could sample many of their devices, completely free. Only recently have they started to charge shipping cost. Also, AFAIC, Microchip's website and distribution network blows Atmel's out of the water.