Thats actually a really good rule, the whole point of a league system is to determine who the best teams are, its not fair if one team is so far ahead of the rest, yet can not get promoted by a team that had been markedly worse. There is a chance that the team in 7th could go up in their place, and that team could be 40 points ahead of that come next weekend.
Also Wrexham's home form was unreal this season:
Played: 22
Won:21
Drew: 1
Lost:0
Goals Scored: 71
Goals Conceded: 18
Goal Difference: +53