> It would have been better to give them nothing rather than a "cheap" gift?
Yes. Giving nothing doesn't give any indication of value - maybe the work is very highly valued but it's not Yahoo's policy to compensate. Fair enough.
Giving a cheap gift attaches a very particular value.
"rewards undermine the intrinsic motivation of volunteers."
"a large literature in social psychology [emphasizes] that external rewards can undermine the intrinsic motivation for an activity"
Yes. Giving nothing doesn't give any indication of value - maybe the work is very highly valued but it's not Yahoo's policy to compensate. Fair enough.
Giving a cheap gift attaches a very particular value.
There is a body of research on this, e.g. http://ideas.repec.org/p/zur/iewwpx/007.html
"rewards undermine the intrinsic motivation of volunteers." "a large literature in social psychology [emphasizes] that external rewards can undermine the intrinsic motivation for an activity"