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 of 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).
Daniel Case