Though if you work it out on a daily basis (using 5 days to the week, 22 to the month and 260 to the year, which is the calculation Ticket Offices use when paying out Void Day refunds for those TOCs still declaring same), sometimes season ticket holders are paying less than Advance ticket holders on a per journey basis (and almost always less than a walk-up ticket, with the exception of some contra-peak flows)!
For example: An Annual Season from Swindon to London is £8000, or £30.77 a day. There are only four generally available "tiers" of Advance fares priced lower than this (£11.60, £12.20, £14.40 and £15.00, respectively) and all of the walk-up fares are significantly more expensive.
So, playing devil's advocate, why should a season ticket holder have more "right" to a seat than the vast majority of non-season holders who've paid a higher fare for their journey?