Do 4-bit CPUs still outsell 32-bit CPUs in unit volume?
The reason that 4 bit CPUs beat out the high end processors at the time was primarily due to their use in watches and clocks.  A 4 bit CPU, running in BCD mode (ie, each 4 bits was one 0-9 digit), is very optimal for clock and timing applications, and in volume they are nearly as cheap as transistors.  They are used in many other very low cost, very high volume applications.

I don't know whether they still beat 32 bit CPUs, however the trend has been going up steeply for 32 bit processors due to cell phones and portable computing devices. I can't imagine that 4 bit CPUs are going up at the same rate.

64 bit CPUs are still largely related to computers, and are probably still low volume enough that they have not yet eclipsed 4 bit CPU volume.