Yeah but you only ever need to roll a few of them at a time, max. You can get away with having just one, or re-rolling a d6 that comes up as 5 or 6. You don't get crits with d4s so the re-rolls really wouldn't be that big of a deal.
I'm not talking about the d4 deciding if the guys are worth sacrificing - even a chicken is worth tossing under a bus for an extra +1. It's about players getting maximum return for their choices - an actually competent minifig being worth more than a shitty little mook or spider just seems to make sense, and I wouldn't want to place restrictions on players for being able to sacrifice fewer things.

