Interesting that you mention Pompey and it being difficult to get tickets for individual games when they were in the Prem. I have a couple of mates who are Portsmouth fans, and that caused a fair bit of alienation among supporters who didn't get every Saturday off work for instance. If you've got the cash to buy a ST, you don't live too far away and you work Monday to Friday it's fine, but it's important that other people get access to matchday tickets too.
When I was in my early 20s I worked in a shop which meant I got four Saturdays off a year (and a day off on Boxing Day was out of the question) so I could only really go to Tuesday night games. If the ground had already been sold out to ST holders I'd just never have been able to watch Argyle live. Luckily we were absolutely terrible at the time so it was never a problem.