There hasn’t been much incentive for approvals until now: committers could just merge immediately, non-committers would get frustrated because their review doesn’t have any effect. Maybe PRs already reviewed will change that. You can already see that in @tomberek’s efforts for example 
I have thought about counting a merge of a PR that doesn’t have an approval by anybody else as an approval. Some committers use the approval feature before merging, others don’t so I think that would be a fairer question.
That would currently drown out non-committer approvals a bit, but maybe that will change. If people start using the distinction between “reviewer” and “merger” more, just listing the merges for committers doesn’t seem fair either.
Here are some more stats, with new PRs included and merge-without-approval counted as approval. Cutoff at 3 this time, to save space and since it is more unique than 10.
Approvals
- xeji (100)
- matthiasbeyer (63)
- timokau (31)
- tomberek (25)
- worldofpeace (21)
Requests for changes
- timokau (17)
- aanderse (11)
- worldofpeace (7)
- xeji (7)
- matthiasbeyer (6)
Merges
- xeji (112)
- timokau (32)
- ryantm (22)
- worldofpeace (22)
- markuskowa (17)
New PRs
- dtzWill (21)
- matthewbauer (8)
- aanderse (7)
- romildo (7)
- vdemeester (7)
And here is the script I used in case someone wants to tinker. Be warned: its neither pretty nor commentated, but also not very complicated.