I ran a couplecouple of queriesqueries and found the following
Site | Count of Post Reopened| Count of Closed Posts | Percentage of Closed
| | | posts that are re-opend
-------------------------------------------------------------------------------
SO | 2528 | 69498 | 3.64%
P.SE | 281 | 3049 | 9.21%
It would seem that since a higher percentage of closed posts got reopened on P.SE than SO I think the opposite is true. You have a better chance of getting a post reopened on a smaller site.
If you think Moderator vs Community opening is important here's the break down of the #Of voters per reopen. Using this querythis query
Voter P.SE SO
Count
----- ------ -------
1 169 861
2 18 147
3 17 70
4 9 70
5 68 1380
Total 281 2528
Reopens that involved some moderator intervention was about 75% on P.SE and 45% on SO. If you look at only moderator ones its 60% on p.SE vs 34% on SO.
This means that if your going to get your question reopened on P.SE its more likely to include moderation attention than on SO. I don't know if that's important or not.