"The reason many people criticise the tuning of banjos is because most banjos are out of tune. It's an inherent design defect."

Speaking as a banjo player, there is an element of truth here. Banjos don't have compensated bridges, so with three plain strings and one wound (usually), if the bridge is set to give correct intonation for the first and fourth strings, the intonation on the third string is probably out.

I use a moon bridge which helps, and also sometimes do a fine tune by ear after electronic tuning, but it still can be a bit approximate.

I also find that intonation drifts out as the strings age, so unless you compensate by regularly moving the bridge(or replace strings a lot more often than I do), yes you do end up with that traditional off-key banjo sound

nick