Is there an easy way to filter games by this criteria on Steam itself?
Yes, that is the case case with the DRM free Steam games I have played. I guess that this is common among indie games at Steam, but I have not really looked into it.
> Is there an easy way to filter games by this criteria on Steam itself?
Do not think so. I do not think Valve want to dissuade developers to use their DRM.
3rd-party DRM: SecuROM™
4 machine activation limit