Yes, the tough part of most ag equipment design is coming up with something that works in a wide variety of seed size, types and seeding depths, soil types, soil conditions, residue levels and residue conditions not to mention moisture levels from irrigated to very dryland.   

Nowadays there is a lot of work going on to be able to adjust the planter on the go as soil types etc change across the field (which they almost always do). For example my son Joe is working on sensing and control systems that can adjust planter row unit down pressure and separately closing wheel down pressure on the go as the planter crosses a field or fields. While not cheap, this type of control can have a quick payback in many planting operations.

A uniform stand of seedlings that emerge at the same time is the key to profitability in row crop systems. If you don't have a good stand emerging, none of the rest of it makes as much sense. The planter is the key. And as far as planter closing wheels go, I think the Curvetine comes close to planting seed as we do in a garden.