For those who don't know about the global needle business, the issue is that the magnetic force a compass responds to has a vertical component as well as a horizontal component. The amount of the vertical component changes as you move north or south on the earth's surface. If you go too far north or south of the zone your compass is balanced for, the needle will incline enough for one end of it to rub on the compass case, making the needle unreliable and unresponsive.
Compass makers divide the earth into 5 zones. In general, the compass you buy is balanced for the zone you bought it in. You should not assume your compass will be reliable if you take it to another zone. That is, of course, a problem for compass-using folks who travel north and south -- and there are more of those folks today than there used to be.
Suunto has technology that allows it to divide the earth into two zones -- that's what it uses in its hemispheric compasses. It is easier for both Suunto and their customers to only have to worry about which hemisphere they are in (north or south), especially since the compasses have quite a bit of overlap where they both work well.
Suunto has gone beyond that with their global compasses -- those work over the entire earth -- as just one zone. (I'm sure there are issues very near the two magnetic poles themselves; fortunately, that's not where most of us go backpacking or expeditioning).
There are a couple of other advantages to Suunto's technology. For one thing, the technology results in a better than normal settling time for the needle -- that's always a win. The other thing is that the compass can tolerate being 20 degrees off level. That means the compass will work better while you are walking, for example. I would also expect that to mean it may be a better compass for use in watercraft, such as a canoe (think huge Canadian lakes with hundreds of islands).
The above is what I found when I used Google recently -- I do not have domain expertise personally. If you want more information, try Google yourself, and report back to the rest of us what you find. :))