Years ago, I brought home 3" thick granite surface plates. I placed my speakers directly on them without spikes. Floor was concrete slab. Sounded great so I would not say that spikes are always needed.
Is Spiking Necesarry?
I like to move my speakers around a bit for to test how they sound, so I slide them. I have the Proac D48Rs, they are kind of heavy so with the spikes in it makes it tough to move them. I haven't consciously tested or compared the sound with spikes or without them. Does it make a difference?