Is there not also an issue of how the tickets are distributed and how the club pays for them? I think unless the rules have changed (and in these days of electronic ticketing, they need changing) that - for the Premier League - the away club receives some tickets on sale-or return, then any extra allocation requested they are on consignment - i.e. you are committed to paying for them. Even though we always do sell out, I think in the recent past (QPR away last season) the club took less of an allocation than they could have, for fear of being left with unsold tickets they'd have to pay for.
But with electronic ticketing, there's no reason why the away club couldn't continue to sell up until a pre-specified deadline, after which Arsenal could then resell unused blocks as home tickets, within their segragation plans. I know this is a Premier League problem, but imagine the ticketing issues are the same between clubs. Selling tix on consignment to away clubs in this day and age is ridiculous - and they wonder why the atmosphere is a problem.