Carb Studs or Bolts--Any Rhyme or Reason?

Many OEM assemblies have studs in 2 holes and bolts in other 2 holes. Only reason is the carb shape gets in the way so you can't drop a bolt into certain holes, so place a nut on a stud there. Bolts wouldn't work at all 4 but studs would have. Why OEM didn't use 4 studs? Don't know. I'll guess nuts are easier dropped and lost.