hyena64: I just assumed it was to lessen damage to both course
Yep, the hard spikes are quite controversial and supposedly cause damage (and banned on many courses) to greens, so soft spikes are more common. Some also argue that hard spikes help aerate the greens and I have heard complaints that soft spikes cause more compaction so arguments from both sides.
Personally I am happy to play in soft spikes as you really seldom need more grip and they are accepted at more courses. Either or, both are comfortable IMO.