That 2002 statistic might have been a bit surprising, but it wasn't some two bit factoid from USAToday. The author was once an editor for the Microprocessor Report.
If you think back to the technology and prices of the mid-1990's (when many design decisions affecting volumes in the early 2000's were made), a lot of embedded applications were simple and well-suited to 4-bit and 8-bit processors. (Heck, it's still true today for most of the "invisible" processors in use - like the LCD thermostat, or the microwave, or the smart dimming dome light in your car.)
The problem with 16-bit and 32-bit processors back then was that it was needlessly more expensive to provide memory for them. RAM was not cheap back then. And wider RAM was much more expensive for the same capacity. (In fact, the early PC's were quasi-16-bit machines. They had an 8-bit external memory bus.)
Fast forward to this decade, and one key change is that the newer embedded processors have plenty of embedded RAM on-board; thanks in large part to improved semiconductor processes.
Without the external RAM penalty, it's just as easy to grab a 32-bit processors for a new design. And the volumes are there that you don't pay much more for the 32-bit. In fact, for bang-per-buck, the older 8-bit processors are awful for new designs. And, I can't even imagine anyone today would even bother with datasheets for a 4-bit processor.
So, have 4-bit processors died? Given that even soft core processors are 8-bits, I'd say yes. The fun question today is what the split is between 8-bits, 32-bits, and 64-bits.
Circling back to the original question - I used to see "processor yearbooks" that detailed processor offerings from different manufacturers - and they were broken into groups by processor bit size, and whether they were MCU or CPU's. I haven't seen one of those things lately -- I think there's far more players in the market today, many of them from Asia-centric companies that have little or no sales presence in the U.S. Additionally, "processors" may be hidden inside FPGA's so that it would be hard to count them.