Figure 1 is a generic block diagram for a weighing scale. It is not the representation of what Cypress has. Yes, PSoC3 and PSoC5 devices have 20 bit DelSig ADC with which we can achieve 18 up to ENOB. Can you please guide us where did you find this value of precision?
A good overview of design considerations for a weigh scale. Notice though that Figure 1 is showing a 24-bit ADC whereas the DelSig peripheral is up to 20-bits. Also, the article states that "such ADCs (with internal gain amps) can provide about 18 effective numbers of bits" though generally commercial applications would require 16. The Cypress website states the DelSig peripheral gives a precision of up to 0.003% which if I figured right is 15-bits.