It's really just a personal choice of upside vs. floor.
Nemec has the higher floor but a lower ceiling while Jiricek has a lower floor and a higher ceiling.
You just don't find a lot of right handed D with Jiricek's size, skating ability, and attack mindset, on top of being a physical presence on the defensive end.
Nemec has come on lately with production which is nice, he's a smart player, defends well with skating and gap control. Creates by thinking well, just I think there's limitations offensively with not a natural goal scoring instinct and not being as attack oriented in terms of putting pressure on the defense with carrying the puck, skating it around and looking for a breakdown.