Can't tell if srs or not. Most likely these people are mining for the FUN of it. For a lot of us mining for bitcoins, no matter what the difficulty is, draws a form of primal satisfaction similar to watching your HD defragment. 
This
Also I don't pay anything extra for electricity and my computer is on all day anyway so why not have it fire up mining when the system is idle?
I even mine on an old pci card also that I found in my old stuff, it manages like 2mh
Most modern chips use less power when they're idling than when they're running under load... so you're paying more for power to mine even if you normally left your computer on 24/7.