The way I read this is either:
- Free middle set if we have enough remaing seats (i.e. there are free available seats)
OR
- Free middle seats where there is actually a middle set - but no free seat beside you if there are only 2 seats beside each other (because there is no middle seat "avialble"....
OR
- No free middle seats when we use a plane with real business class... such as A340 etc. (that would be then just a legal statement, because someone sued them because of such a case)

Probabbly again the beancouner were active and I can see where they are coming from (altough I do completely disagree!)
In a 3 - 3 Setting 4 out of 6 seats can be sold, which means 67% of seats can be sold
In a 2- 2 setting 2 out of 4 seats can be sold, which is only 50% of capacity...