Build quality of 35 vs 50 is also a factor.
Actually, I was referring to the EF 50/1.8, not the more cheaply built 50/1.8 II. The former was equivalent in build to the 35/2 (metal mount, etc.), and cost close to 50% less.
Ah the old little primes, I have both the 35f/2 and 50f/1.8 MkI and they're still a great team of little primes that'll fit in any bag
Back on topic
5D3, 5D2, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC