One thought: If you shoot 100.000 pictures (whoever may do that) with a DSRL it may be better than producing 365 gallons of developer waste (just do the math: film tank with 500ml capacity, 36 frames. The ration is far worse with 120).
But a serious amateur might shoot 100k frames within a couple of years on a DSLR, then dispose, and upgrade. At my current shooting rate, with 120, 100,000 frames would take 10 years.
'Cows are very fond of being photographed, and, unlike architecture, don't move.' - Oscar Wilde