Phage, you're right. Area denial munitions like that are the key.
But.
Those systems aren't ready and are not cheap.
How secure are they? Can the enemy also block the signal when your tanks are rushing across and re-arm them? Can they turn them off or locate them when they decide to advance?
Can they see them with other equipment and then destroy them?
The Korean situation is that the US govt will not sign the anti-mine treaty due to the millions of mines lining the border to North Korea. They feel that the cost of bad publicity is worth the fact that North Korea will not rush hundreds of tanks across an hour.
Those mines, even though they are in mapped areas are trouble when you want to de-mine them.
Mines swim.
Farmers sometimes say that the only thing the earth is guaranteed to grow is rocks.
The ground is constantly moving stuff around. Places in the Balkans that were mapped out for mines have had their kill zone expanded due to natural movements in the soil.
The mines are no longer in sequences. They are dumb and they kill anyone or thing that applies enough pressure to trigger them.
Some good alternatives are what you spoke of or this thing:
Metal Storm
Aread denial system video: (Real player. Go to site if you want other format)
http://www.metalstorm.com/04_videos/ms_area_denial.rm