There is still some false logic in there.France has more decent clubs than just the 20 Ligue 1, and Portuguese football has a higher average attendance that it otherwise would, by only having 16 teams competing. If we compare like for like, we'd probably be an average attendance of around 8640 for Portugal's top 20 teams. Or perhaps it would be fairer to look at either the top 16 French teams attendances, or possibly the absolute attendance rather than average. The Portuguese league is over just 30 games, the French 38...They have more people than the rest besides Germany and Russia so that shouldn't be a factor.
Portugal 10 million => 10800 average attendance
France 65 million => 20000 average attendance
There are lots of factors that should be taken into account really. France is a huge place, so the top 20 teams aren't going to properly represent every community. The 16 Portuguese teams should represent more of Portugal than the 20 French teams.
I think the best statistic would be to just compare the top 16 French teams with the 16 Portuguese teams; but I dont have the capacity to do that at the moment. http://www.soccerstats.com/attendance.asp?league=france_2013