I noticed that at the 1st post of a thread the "Like" button is available. Considering that members usually open discussions to ASK, I can't see usefulness of enabling such a feature there. Just my oppinion.
Perhaps a member would like to identify a particularly well written question? It probably isn't worth the programming effort to dynamically enable/disable that feature.
LIKE can mean different things in different contexts as I see it. I don't know of any formal description of its intended use. Obviously, if you find something useful, LIKE it. But I also use it as a quick acknowledgement - of a relevant post, a quick appreciation of something said or, in the case of a new poster, just as a quick note that they are doing it right.