This issue is about adding two settings to the configuration file:
regions:
....
default:
...
tnt: false
fire: false
It should work like the pvp: false setting, so that
ignition:
block-tnt: on
block-lighter: on
work like a global setting (like pvp=off in server.properties) and tnt and fire (through lighter) would be denied everywhere, regardless of other settings.
When these two are set to off, and the requested settings above are set to false, tnt and fire are globally enabled but denied everywhere, except in regions where explicitly set to allow with the related flag (+tnt and +fire or +lighter for example).

See posts #880 till #884: http://forums.bukkit.org/threads/sec-worldguard-v3-2-2-protect-cuboids-blacklist-fire-spread-blocking-works.790/page-30#post-40080

Would love that too !
I think that default regions should have the same properties as normal ones.