Hmm, I think the list of most-thanked people actually
tells us more about
who is doing the thanking. I see at least 5 names on that list that I
recognise from my watchlist and therefore I may have thanked (statistically
unlikely I would recognise 5 out of 10 random Wikipedia user names) and 2
them I know I have thanked many times as we interact regularly in two
different topic areas.
My takeaway from that list, for enwiki at least, is that at least a few of
the names on it are admins very active in anti-vandalism work, so I would
guess a fair amount of the thanks they get are from people who've made
reports to AIV and are thankful for the ensuing block of the vandal (based
on my experience from when I was doing that heavily).